docs: add new features page

Author: insertish

doc/src/SUMMARY.md

@@ -2,6 +2,7 @@
 
 - [Introduction](./hello.md)
 - [Project Structure]()
+- [Creating new API features](./new_features.md)
 - [Testing]()
   - [Writing a new database test]()
   - [Writing a new API test]()

doc/src/new_features.md

@@ -0,0 +1,15 @@
+# New API features
+
+New API features must be documented where appropriate, this document aims to cover everywhere you need to update for new features.
+
+Before writing new API features, generally a good idea to:
+
+- Consult with other developers in the [Revolt Developers space](https://rvlt.gg/API)
+- If it's a relatively big feature, also [write an RFC](https://github.com/revoltchat/rfcs)
+
+When your feature is ready to release, ensure to:
+
+- Update backend documentation (what you're reading now!) if applicable
+- Update the [developers documentation](https://github.com/revoltchat/wiki) if applicable
+- Update the Feature Matrix (or ask someone that can to do so)
+- Ensure it is properly listed in the backend release changelog