Add docs for ENV variables take gitlab:uploads:check rake task supports

doc/administration/raketasks/check.md

@@ -96,6 +96,19 @@ sudo gitlab-rake gitlab:uploads:check
 sudo -u git -H bundle exec rake gitlab:uploads:check RAILS_ENV=production
 ```
 
+This task also accepts some environment variables which you can use to override
+certain values:
+
+Variable | Type | Description
+-------- | ---- | -----------
+`BATCH`   | integer  | Specifies the size of the batch. Defaults to 200.
+`ID_FROM` | integer  | Specifies the ID to start from, inclusive of the value.
+`ID_TO`   | integer  | Specifies the ID value to end at, inclusive of the value.
+
+```bash
+sudo gitlab-rake gitlab:uploads:check BATCH=100 ID_FROM=50 ID_TO=250
+```
+
 ## LDAP Check
 
 The LDAP check Rake task will test the bind_dn and password credentials