Add manual DB backup instructions

docs/operators/handbook.md

@@ -331,3 +331,26 @@ If you're app [supports backup/restore](/handbook/#how-do-i-configure-backuprest
 
 With `abra`, you can simply run `abra app backup ...` & `abra app restore ...`.
 Pass `-h` for more information on the specific flags & arguments.
+
+## How do I take a manual database backup?
+
+MySQL / MariaDB:
+
+```
+abra app run foo.bar.com db mysqldump -u root <database> | gzip > ~/.abra/backups/foo.bar.com_db_`date +%F`.sql.gz
+```
+
+Postgres:
+
+```
+abra app run foo.bar.com db pg_dump -u root <database> | gzip > ~/.abra/backups/foo.bar.com_db_`date +%F`.sql.gz
+```
+
+If you get errors about database access:
+- Make sure you've specified the right database user (`root` above) and db name
+- If you have a database password set, you might need to load it from a secret,
+    something like this:
+
+```
+abra app run foo.bar.com db bash -c 'mysqldump -u root -p"$(cat /run/secrets/db_oot_password)" <database>' | gzip > ~/.abra/backups/foo.bar.com_db_`date +%F`.sql.gz
+```