Improve postgres PGDATA documentation

postgres/content.md

@@ -95,7 +95,18 @@ See the PostgreSQL documentation on [`pg_hba.conf`](https://www.postgresql.org/d
 
 ### `PGDATA`
 
-This optional variable can be used to define another location - like a subdirectory - for the database files. The default is `/var/lib/postgresql/data`, but if the data volume you're using is a filesystem mountpoint (like with GCE persistent disks), Postgres `initdb` recommends a subdirectory (for example `/var/lib/postgresql/data/pgdata` ) be created to contain the data.
+This optional variable can be used to define another location - like a subdirectory - for the database files. The default is `/var/lib/postgresql/data`. If the data volume you're using is a filesystem mountpoint (like with GCE persistent disks) or remote folder that cannot be chowned to the `postgres` user (like some NFS mounts), Postgres `initdb` recommends a subdirectory be created to contain the data.
+
+For example:
+
+```console
+$ docker run -d \
+	-name some-postgres \
+	-e POSTGRES_PASSWORD=mysecretpassword \
+	-e PGDATA=/var/lib/postgresql/data/pgdata \
+	-v /custom/mount:/var/lib/postgresql/data \
+	%%IMAGE%%
+```
 
 This is an environment variable that is not Docker specific. Because the variable is used by the `postgres` server binary (see the [PostgreSQL docs](https://www.postgresql.org/docs/11/app-postgres.html#id-1.9.5.14.7)), the entrypoint script takes it into account.