docs: list retroachievements provider in readme and env example

Author: DevYukine

.env.example

@@ -49,6 +49,16 @@ MOBYGAMES_API_KEY=YOUR_MOBYGAMES_API_KEY
 # release asset when omitted.
 # OPENVGDB_METADATA_URL=https://github.com/OpenVGDB/OpenVGDB/releases/latest/download/openvgdb.zip
 
+# RetroAchievements requires a username + web API key (free; get one from
+# https://retroachievements.org/controlpanel.php). Both must be set together.
+# When enabled the provider bulk-imports every RA system, game, and MD5 hash
+# once per cycle (one API call per system, ~70 calls total with a 1s courtesy
+# delay between calls) and matches local ROMs by MD5 hash first then by name.
+# Custom-hash consoles (PS1, GameCube/DS, Dreamcast/Saturn, PCE-CD, 3DO,
+# Arcade) only match by name; plain-MD5 consoles match by hash.
+# RETROACHIEVEMENTS_USERNAME=YOUR_RA_USERNAME
+# RETROACHIEVEMENTS_API_KEY=YOUR_RA_WEB_API_KEY
+
 # Pepper used for HMAC-SHA256 hashing of API keys. Generate with `openssl rand -hex 32`.
 # Must be at least 16 raw bytes (32 hex chars). Treat like a production secret.
 API_KEY_PEPPER=REPLACE_WITH_OUTPUT_OF_openssl_rand_hex_32

README.md

@@ -28,6 +28,7 @@ The public API is available at [playmatch.retrorealm.dev](https://playmatch.retr
 - [x] Support for LaunchBox as metadata provider (bulk metadata import, opt-in via `LAUNCHBOX_ENABLED`)
 - [x] Support for OpenVGDB as metadata provider (offline SQLite hash matching, opt-in via `OPENVGDB_ENABLED`)
 - [x] Support for EmuReady as metadata provider (id-mapping only, opt-in via `EMUREADY_ENABLED`)
+- [x] Support for RetroAchievements as metadata provider (bulk import via API, MD5 hash matching plus name fallback, opt-in via `RETROACHIEVEMENTS_USERNAME` + `RETROACHIEVEMENTS_API_KEY`)
 
 ### Planned