docs(readme): use common CONTRIBUTING.md

CONTRIBUTING.md

@@ -1,35 +1,3 @@
 ## Contributing
 
-Here are listed all the ways you can contribute to the project.
-
-### Issues
-
-If you encounter an issue, you can create a
-[Github issue](https://github.com/ManoManoTech/homer/issues/new).
-
-### Develop
-
-#### Necessary environment variables
-
-- **GITLAB_SECRET_TOKEN**: from Gitlab project webhooks, to validate incoming
-  Gitlab requests.
-- **GITLAB_TOKEN**: to interact with the Gitlab API.
-- **POSTGRES_HOST**: host of the PostgreSQL database.
-- **POSTGRES_PASSWORD**: password used when connecting to the PostgreSQL
-  database.
-- **POSTGRES_PORT**: port where the PostgreSQL database listens.
-- **POSTGRES_USER**: username used when connecting to the PostgreSQL database.
-- **SLACK_BOT_USER_O_AUTH_ACCESS_TOKEN**: to publish Slack messages.
-- **SLACK_SIGNING_SECRET**: to validate incoming Slack requests.
-
-#### Use Ngrok
-
-```bash
-ngrok http localhost:3000
-```
-
-#### Start the database locally
-
-```bash
-docker compose up -d
-```
+See [Contributing to this repository](https://github.com/ManoManoTech/ALaMano/blob/master/CONTRIBUTING.md).

README.md

@@ -159,22 +159,22 @@ Be sure to have all those installed:
 
 Create a `.env` file containing the following variables:
 
-- `GITLAB_SECRET=`
+- `GITLAB_SECRET`
 
   This is a user generated secret, so you can put any value.
 
   It will be used later to set up Gitlab webhooks to allow Homer to verify
   that Gitlab→Homer calls are authentic.
 
-- `GITLAB_TOKEN=`
+- `GITLAB_TOKEN`
 
   If you don't already have one, you need to create a project access token on
   Gitlab by following the
   [dedicated documentation](https://docs.gitlab.com/ee/user/project/settings/project_access_tokens.html#create-a-project-access-token).
 
   This token allows Homer to use the Gitlab API.
 
-- `SLACK_SIGNING_SECRET=`
+- `SLACK_SIGNING_SECRET`
 
   - Go to the [Slack apps page](https://api.slack.com/apps/) of your
     organisation.
@@ -185,7 +185,7 @@ Create a `.env` file containing the following variables:
 
   This secret allows Homer to verify that Slack→Homer calls are authentic.
 
-- `SLACK_BOT_USER_O_AUTH_ACCESS_TOKEN=`
+- `SLACK_BOT_USER_O_AUTH_ACCESS_TOKEN`
 
   - Go to the [Slack apps page](https://api.slack.com/apps/) of your
     organisation.
@@ -198,6 +198,14 @@ Create a `.env` file containing the following variables:
 
     ![OAuth token](docs/assets/slack/oauth-token.png)
 
+If you want Homer to connect to an **external PostgreSQL database**, you can set
+the following variables:
+
+- `POSTGRES_HOST`: host of the database.
+- `POSTGRES_PASSWORD`: password used when connecting to the database.
+- `POSTGRES_PORT`: port where the database listens.
+- `POSTGRES_USER`: username used when connecting to the database.
+
 ### 5. Install and run
 
 ```bash