feat(scaffolder-backend,doc): Adding Documentation for plugin

Signed-off-by: Thomas Viaud <t.viaud@elsevier.com>

.changeset/old-horses-brake.md

@@ -0,0 +1,6 @@
+---
+'@backstage/plugin-scaffolder-backend': patch
+---
+
+Fix GithubPR built-in action `credentialsProvider.getCredentials` URL.
+Adding Documentation for GitHub PR built-in action.

plugins/scaffolder-backend/README.md

@@ -1,7 +1,18 @@
-# Title
+# Scaffolder Backend
 
 Welcome to the scaffolder plugin!
 
-## Sub-section 1
+## Jobs
+Documentation for `Jobs` here
+## Stages
+Documentation for `Stages` here
+## Tasks
+Documentation for `Tasks` here
 
-## Sub-section 2
+## Actions
+### Built-in:
+* #### GitHub Pull Request
+    * Minimum permissions required for GitHub App for creating a Pull Request with the built-in action:
+        - Read and Write permissions for `Contents`.
+        - Read and write permissions for `Pull Requests` and `Issues`.
+        - Read permissions on `Metadata`.