Move backend guides away from Database section

"Code comments" and "Renaming features" guides were wrongly added to the
Database Best Practices section. This commits moves them back to the
Backend guides

doc/development/README.md

@@ -98,6 +98,8 @@ Complementary reads:
 - [Application limits](application_limits.md)
 - [Redis guidelines](redis.md)
 - [Rails initializers](rails_initializers.md)
+- [Code comments](code_comments.md)
+- [Renaming features](renaming_features.md)
 
 ## Performance guides
 
@@ -150,9 +152,7 @@ Complementary reads:
 - [Verifying database capabilities](verifying_database_capabilities.md)
 - [Database Debugging and Troubleshooting](database_debugging.md)
 - [Query Count Limits](query_count_limits.md)
-- [Code comments](code_comments.md)
 - [Creating enums](creating_enums.md)
-- [Renaming features](renaming_features.md)
 
 ### Case studies