Add details in READMEs for react-devtools local developement (facebook#24148)

* Add details in READMEs for react-devtools local developement

* typo

* update yarn for release script

Author: mondaychen

packages/react-devtools-inline/README.md

@@ -348,10 +348,14 @@ To build dependencies from source, run the following command from the root of th
 yarn build-for-devtools
 ```
 ### Download from CI
-To use the latest build from CI, run the following command from the root of the repository:
+To use the latest build from CI, go to `scripts/release/` and run the following commands:
 ```sh
-./scripts/release/download-experimental-build.js
+yarn
+./download-experimental-build.js --commit=main
 ```
+
+Please note that you might need to [create a Circle CI API Token](https://circleci.com/docs/2.0/managing-api-tokens/) and set up an environment variable `CIRCLE_CI_API_TOKEN`.
+
 ## Build steps
 Once the above packages have been built or downloaded, you can watch for changes made to the source code and automatically rebuild by running:
 ```sh

packages/react-devtools-shell/README.md

@@ -2,11 +2,13 @@ Harness for testing local changes to the `react-devtools-inline` and `react-devt
 
 ## Development
 
-This target should be run in parallel with the `react-devtools-inline` package. The first step then is to run that target following the instructions in the [`react-devtools-inline` README](https://github.com/facebook/react/blob/main/packages/react-devtools-inline/README.md).
+This target should be run in parallel with the `react-devtools-inline` package. The first step then is to run that target following the instructions in the [`react-devtools-inline` README's local development section](https://github.com/facebook/react/tree/main/packages/react-devtools-inline#local-development).
 
 The test harness can then be run as follows:
 ```sh
 cd packages/react-devtools-shell
 
 yarn start
 ```
+
+Once you set both up, you can view the test harness with inlined devtools in browser at http://localhost:8080/