[Google TTS] Update README.md (openhab#15637)

* Update README.md

I had some struggles with setting up google TTS, got it to work eventually and now update the README to help users in the future.

This commit includes updating the information, including necessary tips, formatting und some minor details

Signed-off-by: Felix Schneider <fs@felix-schneider.org>

bundles/org.openhab.voice.googletts/README.md

@@ -12,23 +12,25 @@ You can find pricing information on the [documentation page](https://cloud.googl
 
 * [Obtaining Credentials](#obtaining-credentials)
 * [Configuration](#configuration)
-* [Voice Configuration](#voice-configuration)
+* [Voice Configuration](#default-text-to-speech-and-voice-configuration)
 
 <!-- /MarkdownTOC -->
 
 ## Obtaining Credentials
 
 Before you can integrate this service with your Google Cloud Text-to-Speech, you must have a Google API Console project:
 
-* Select or create a GCP project. [link](https://console.cloud.google.com/cloud-resource-manager)
-* Make sure that billing is enabled for your project. [link](https://cloud.google.com/billing/docs/how-to/modify-project)
-* Enable the Cloud Text-to-Speech API. [link](https://console.cloud.google.com/apis/dashboard)
-* Set up authentication:
-  * Go to the "APIs & Services" -> "Credentials" page in the GCP Console and your project. [link](https://console.cloud.google.com/apis/credentials)
-  * From the "Create credentials" drop-down list, select "OAuth client ID".
-  * Select application type "Web application" and enter a name into the "Name" field.
-  * Add "https://www.google.com" to the "Authorized redirect URIs".
-  * Click Create. A pop-up appears, showing your "client ID" and "client secret".
+1. Select or create a Google Cloud project ([link](https://console.cloud.google.com/cloud-resource-manager))
+2. Make sure that billing is enabled for your project ([link](https://cloud.google.com/billing/docs/how-to/modify-project))
+3. Enable the `Text-to-Speech API` ([link](https://console.cloud.google.com/apis/dashboard))
+  * Don't mistake with the `Speech-to-Text API`
+4. Set up authentication:
+  1. Go to the `APIs & Services` -> `Credentials` page in the GCP Console and your project ([link](https://console.cloud.google.com/apis/credentials))
+  2. From the `Create credentials` drop-down list, select `OAuth client ID`.
+  3. Select application type `Web application` and enter a name into the `Name` (e.g. `OpenHAB TTS`) field.
+  4. Add `https://www.google.com` to the `Authorized redirect URIs`.
+    * Watch out for trailing spaces in the URL! E.g. when using the copy url feature in the context menu of Google Chrome it appends a slash (`https://www.google.com` becomes `https://www.google.com`) and the steps afterwards fail.
+  5. Click Create. A pop-up appears, showing your "client ID" and "client secret".
 
 ## Configuration
 
@@ -37,12 +39,12 @@ Using your favorite configuration UI to edit **Settings / Other Services - Googl
 * **Client Id** - Google Cloud Platform OAuth 2.0-Client Id.
 * **Client Secret** - Google Cloud Platform OAuth 2.0-Client Secret.
 * **Authorization Code** - This code is used once for retrieving the Google Cloud Platform access and refresh tokens.
-**Please go to your browser ...**
-[https://accounts.google.com/o/oauth2/v2/auth?scope=https://www.googleapis.com/auth/cloud-platform&access_type=offline&prompt=consent&include_granted_scopes=true&response_type=code&redirect_uri=https://www.google.com&client_id=<clientId>](https://accounts.google.com/o/oauth2/v2/auth?scope=https://www.googleapis.com/auth/cloud-platform&access_type=offline&prompt=consent&include_granted_scopes=true&response_type=code&redirect_uri=https://www.google.com&client_id=<clientId>) (replace `<clientId>` by your Client Id)
-**... to generate an authorization code and paste it here**.
-After your browser has been redirected to https://www.google.com, the authorization code will be set in the browser URL as value of the "code" URL query parameter.
-After initial authorization, this code is not needed anymore.
-It is recommended to clear this configuration parameter afterwards.
+  1. Go to `OAuth consent screen` ([link](https://console.cloud.google.com/apis/credentials/consent)) and set the `publishing status` to `production` to activate the created project.
+  2. Wait a few minutes. The step before takes some time to go live. Sometimes it is necessary to wait a few hours, so you can try after some minutes, if it doesn't work, try again the next day.
+  3. Go to your browser and access the following URL to generate an authorization code
+[https://accounts.google.com/o/oauth2/v2/auth?scope=https://www.googleapis.com/auth/cloud-platform&access_type=offline&prompt=consent&include_granted_scopes=true&response_type=code&redirect_uri=https://www.google.com&client_id=<clientId>](https://accounts.google.com/o/oauth2/v2/auth?scope=https://www.googleapis.com/auth/cloud-platform&access_type=offline&prompt=consent&include_granted_scopes=true&response_type=code&redirect_uri=https://www.google.com&client_id=CLIENTID) (replace `CLIENTID` at the end by your Client Id)
+  4. After your browser has been redirected to https://www.google.com, the authorization code will be set in the browser URL as value of the "code" URL query parameter (e.g. `https://www.google.com/?code=XXXXXXXXXX&scope=https://www.googleapis.com/auth/cloud-platform` --> `XXXXXXXXXX`)
+  5. After initial authorization, this code is not needed anymore. It is recommended to clear this configuration parameter afterwards.
 * **Pitch** - The pitch of selected voice, up to 20 semitones.
 * **Volume Gain** - The volume of the output between 16dB and -96dB.
 * **Speaking Rate** - The speaking rate can be 4x faster or slower than the normal rate.
@@ -75,3 +77,12 @@ In case you would like to setup these settings via a text file, you can edit the
 org.openhab.voice:defaultTTS=googletts
 org.openhab.voice:defaultVoice=googletts:XXX
 ```
+You can see the available voices by entering `voice voices` in the karaf console
+```shell
+openhab> voice voices
+  ...
+  Google Cloud - Deutsch (Deutschland) - de-DE-Standard-C (googletts:deDEStandardC)
+  ...
+  Google Cloud - Englisch (Vereinigte Staaten) - en-US-Neural2-A (googletts:enUSNeural2A)
+  ...
+```