docs: add additional prereqs for github register existing component GPT

templates/github/register-github-component/README.md

@@ -4,11 +4,33 @@ This template is intended to be used as a starting point for registering an exis
 
 ## Prerequisites
 
+- Please ensure the github host is added to the `app-config.yaml` file in the backstage instance
+- If using a github enterprise instance, please make sure the `apiBaseUrl` is set correctly:
+
+  ```yaml
+  integrations:
+    gitlab:
+      - host: github.mycompany.com # this must match the hostname of your gitlab instance
+        token: my-github-token # You can use a token or a github app (app will take precedence)
+        apps:
+          - appId: app-id
+            clientId: client-id
+            clientSecret: client-secret
+            webhookSecret: webhook-secret
+            privateKey: |
+              -----BEGIN RSA PRIVATE KEY-----
+              ...Key content...
+              -----END RSA PRIVATE KEY-----
+        apiBaseUrl: https://github.mycompany.com/api/v3 # This field is optional if host is `github.com`
+        # apiBaseUrl: https://api.github.mycompany.com # This is also a potential api base url for github enterprise
+  ```
+
 ### Required GitHub permissions
 
 The GitHub application or access token needs to have the following permissions:
 
 - **Repository permissions**
+
   - **Contents**: **_Read & write_** - To be able to create a new branch and push files new `catalog-info.yaml` file into it.
   - **Pull requests**: **_Read & write_** - To be able to create pull requests with generated `catalog-info.yaml`.
   - **Commit statuses**: **_Read-only_** - To be able to clone private repositories.