docs: update GitHub spelling

Author: wei

README.md

@@ -4,15 +4,15 @@ A GitHub Action for syncing between two independent repositories using **force p
 
 
 ## Features
- * Sync branches between two Github repositories
+ * Sync branches between two GitHub repositories
  * Sync branches to/from a remote repository
- * Github action can be triggered on a timer or on push
+ * GitHub action can be triggered on a timer or on push
  * To sync with current repository, please checkout [wei/github-sync](https://github.com/marketplace/actions/github-sync)
 
 
 ## Usage
 
-### Github Actions
+### GitHub Actions
 ```
 # File: .github/workflows/repo-sync.yml