Document manual.toml is ordered alphabetical (#955)

Author: raboof

README.md

@@ -94,7 +94,7 @@ You may need to manually edit `frontend/src/Search.elm` to use the right index.
 
 ## Adding flakes
 
-To add your own flakes to the search index edit [./flakes/manual.toml](./flakes/manual.toml).
+To add your own flakes to the search index edit [./flakes/manual.toml](./flakes/manual.toml), keeping the alphabetical ordering.
 
 Possible types are `github`, `gitlab`, `sourcehut`, and `git` (which is the fallback for any kind of git repository but requires to set a revision key manually as of now).