docs: update README with usage instructions and required secrets for APICURON action

Author: Mehdi-SK

README.md

@@ -1,3 +1,14 @@
 # APICURON commit reporter
 
 A GitHub Action that reports pushes to your repository to APICURON, associating them with user ORCIDs 
+
+## Usage
+### Setup
+
+1. **Add Secrets to Repository**:
+   - Go to Repository Settings → Secrets → Actions
+   - Add these required secrets:
+     - `REPORT_API_ENDPOINT`: APICURON report API URL
+     - `REPORT_API_TOKEN`: APICURON API auth token
+     - `USER_INFO_SERVICE_ENDPOINT`: ORCID lookup service URL
+     - `USER_INFO_SERVICE_TOKEN`: ORCID service auth token