Add sample backup and restore command for a PostgreSQL Docker container.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

docs/topics/backups.rst

@@ -4,12 +4,46 @@ Backups
 
 To backup your install of Mayan EDMS just copy the actual document files and
 the database content. If you are using the default storage backend, the
-document files should be found in ``mayan/media/document_storage/``.
+document files should be found in the ``media`` folder of your installation.
 
 To dump the content of your database manager refer to the documentation chapter
 regarding database data "dumping".
 
-Example:
+Here is an example of how to perform a backup and a restore of a PostgreSQL
+Docker container.
+
+To backup a PostgreSQL Docker container::
+
+    docker exec <container name> pg_dump -U <database user> -Fc -c <database name> > dump_`date +%Y-%m-%d"_"%H-%M-%S`.dump
+
+Example::
+
+    docker exec mayan-edms-db pg_dump -U mayan -Fc -c mayan > date +%Y-%m-%d"_"%H-%M-%S`.dump
+
+This will produce a compressed dump file with the current date and time as the filename.
+
+To restore a PostgreSQL Docker container::
+
+    docker exec -i <container name> pg_restore -U <database user> -d <database name> < <dump file>
+
+Since it is not possible to drop a currently open PostgreSQL database, this
+command must be used on a new and empty PostsgreSQL container.
+
+Example::
+
+    docker run -d \
+    --name mayan-edms-pg-new \
+    --restart=always \
+    -p 5432:5432 \
+    -e POSTGRES_USER=mayan \
+    -e POSTGRES_DB=mayan \
+    -e POSTGRES_PASSWORD=mayanuserpass \
+    -v /docker-volumes/mayan-edms/postgres-new:/var/lib/postgresql/data \
+    -d postgres:9.5
+
+    docker exec -i mayan-edms-pg-new pg_restore -U mayan -d mayan < 2018-06-07_17-09-34.dump
+
+More information at:
 
  - Postgresl: http://www.postgresql.org/docs/current/static/backup.html
  - MySQL: https://dev.mysql.com/doc/refman/5.7/en/mysqldump.html