add RFC5 to RFC index

Author: tomkralidis

docs/development/rfc/index.md

@@ -14,3 +14,4 @@ the project.
 * [RFC2: Dependency policy](2)
 * [RFC3: Architectural Decision Records](3)
 * [RFC4: GitHub Issue and Pull Request management](4)
+* [RFC5: Enhanced data limit handling](5)