Add details to README about PAT required permissions (#167)

README.md

@@ -92,7 +92,10 @@ Running `./gradlew upgradeGradleWrapperXXX` will:
 - If changes occurred
   - create a specific branch
   - commit and push the branch
-  - create a pull request on Github, it requires a Github access token, passed with `WRAPPER_UPGRADE_GIT_TOKEN` environment variable.
+  - create a pull request on GitHub, it requires a GitHub personal access token (PAT), passed with `WRAPPER_UPGRADE_GIT_TOKEN` environment variable.
+    This token is used to get the existing PRs on the repo and create one if needed, hence it requires:
+      - the `repo` scope for a classic PAT
+      - read-write permissions for "Pull requests" on the relevant repos for a fine-grained PAT
 
 Note that a check is done first to make sure the branch does not exist yet. That way you can run `upgradeGradleWrapperAll` and `upgradeMavenWrapperAll` periodically with a cron, CI job... a bit like dependabot does for upgrading libs.
 
@@ -120,7 +123,7 @@ wrapperUpgrade {
 | Field                        | description                                                                                                                                                      |
 |:-----------------------------|:-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `name`                       | A name identifying the upgrade, it can be different from the project name, for example when you need to upgrade multiple gradle projects in the same git project |
-| `repo`                       | The Github repository to clone, format 'organization/project`                                                                                                    |
+| `repo`                       | The GitHub repository to clone, format 'organization/project`                                                                                                    |
 | `dir`                        | The directory inside the project base directory to run the gradle or maven upgrade in                                                                            |
 | `baseBranch`                 | The git branch to checkout and that the pull request will target                                                                                                 |
 | `options.gitCommitExtraArgs` | List of additional git commit arguments                                                                                                                          |