add comment on -R

docker/README.md

@@ -94,7 +94,7 @@ The image contains these directories:
 | Docker Environment Var. | Default value | Description |
 | ----------------------- | ------------- | ----------- |
 `SYNC_PERIOD_MINUTES` | 10 | Period of automatic synchronization (i.e. mirroring + reindexing) in minutes. Setting to `0` will disable periodic syncing (the sync after container startup will still be done).
-`INDEXER_OPT` | empty | pass **extra** options to OpenGrok Indexer. The default set of indexer options is: `--remote on -P -H -W`. For example, `-i d:vendor` will remove all the `*/vendor/*` files from the index. You can check the indexer options on https://github.com/oracle/opengrok/wiki/Python-scripts-transition-guide
+`INDEXER_OPT` | empty | pass **extra** options to OpenGrok Indexer. For example, `-i d:vendor` will remove all the `*/vendor/*` files from the index. You can check the indexer options on https://github.com/oracle/opengrok/wiki/Python-scripts-transition-guide. The default set of indexer options is: `--remote on -P -H -W`. Do not add `-R` as it is used internally. Rather, see below for the `READONLY_CONFIG_FILE` environment variable.
 `NOMIRROR` | empty | To avoid the mirroring step, set the variable to non-empty value.
 `URL_ROOT` | `/` | Override the sub-URL that OpenGrok should run on.
 `WORKERS` | number of CPUs in the container | number of workers to use for syncing (applies only to setup with projects enabled)