Fixes some @NonNull warnings.

.env.example

@@ -16,6 +16,7 @@ MINECRAFT_BACKUP_PATH=./backups
 # Release version is read from Gradle's Git-sensitive semantic version and checked against the jar's plugin.yml.
 MODRINTH_TOKEN=
 MODRINTH_PROJECT_ID=metropolis-builder
+# Optional Markdown override; empty generates notes from commits since the last tag.
 MODRINTH_CHANGELOG=
 MODRINTH_GAME_VERSIONS=26.2
 MODRINTH_LOADERS=paper