docs(en): add link

Author: xchopin

docs/en/developer/index.md

@@ -2,7 +2,7 @@
 Contributing to the open source project.
 
 * Contributor Guidelines
-* Coding Standards
+* [Coding Standards](coding_standards.md)
 * Using Maven for development purposes
 * [Automated Tests](tests.md)
 * Run OpenLRW through Docker

docs/en/index.md

@@ -6,7 +6,7 @@ OpenLRW is a free and open source Learning Record Warehouse provided by the Aper
 
 ## Table of Contents
  * Administrator Guide
- * Developer Guide
+ * [Developer Guide](developer/index.md)
  * API Reference
  * External Resources