Add an "arbitrary user" section to MySQL

mysql/content.md

@@ -176,6 +176,17 @@ If the application you're trying to connect to MySQL does not handle MySQL downt
 
 If you start your `%%IMAGE%%` container instance with a data directory that already contains a database (specifically, a `mysql` subdirectory), the `$MYSQL_ROOT_PASSWORD` variable should be omitted from the run command line; it will in any case be ignored, and the pre-existing database will not be changed in any way.
 
+## Running as an arbitrary user
+
+If you know the permissions of your directory are already set appropriately (such as running against an existing database, as described above) or you have need of running `mysqld` with a specific UID/GID, it is possible to invoke this image with `--user` set to any value (other than `root`/`0`) in order to achieve the desired access/configuration:
+
+```console
+$ mkdir data
+$ ls -lnd data
+drwxr-xr-x 2 1000 1000 4096 Aug 27 15:54 data
+$ docker run -v "$PWD/data":/var/lib/mysql --user 1000:1000 --name some-%%REPO%% -e MYSQL_ROOT_PASSWORD=my-secret-pw -d %%IMAGE%%:tag
+```
+
 ## Creating database dumps
 
 Most of the normal tools will work, although their usage might be a little convoluted in some cases to ensure they have access to the `mysqld` server. A simple way to ensure this is to use `docker exec` and run the tool from the same container, similar to the following: