Add code comments to make sure Rust <> JS "reserved usernames" are mi…

…rrored

Summary:
adding comments to help ensure the two lists stay in sync

Note that I could not add comments to the actual reserved_usernames.json file
since comments aren't allowed in JSON notation

Depends on D8481

Test Plan: N/A, just comments

Reviewers: ashoat, jon

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8482

lib/utils/reserved-users.js

@@ -1,6 +1,7 @@
 // @flow
 
-// All entries in this list must be lowercase!!
+// All entries in this list must be lowercase and must also be included in
+// `services/identity/reserved_usernames.json`!!
 const reservedUsernamesSet: $ReadOnlySet<string> = new Set([
   // Additional Reserved Keywords
   'comm',

services/identity/src/config.rs

@@ -75,6 +75,8 @@ fn get_server_setup_from_file<P: AsRef<path::Path>>(
 }
 
 fn get_reserved_usernames_set() -> Result<HashSet<String>, Error> {
+  // All entries in `reserved_usernames.json` must be lowercase and must also be
+  // included in `lib/utils/reserved-users.js`!!
   let contents = include_str!("../reserved_usernames.json");
   let reserved_usernames: Vec<String> = serde_json::from_str(contents)?;