Adds pg instructions.

operators/postgres.md

+# Postgres Operator
+
+## When space if full 
+
+https://www.postgresql.fastware.com/blog/how-to-solve-the-problem-if-pg_xlog-is-full
+
+### To prevent full space
+
+```
+cd /home/postgres/pgdata
+fallocate -l 150M ./to-delete-if-full-1
+fallocate -l 150M ./to-delete-if-full-2
+```
+
+### check /home/postgres/pgdata/pgroot/data/pg_wal
+
+If it is full, it probably means it couldn't upload wals.
+
+check logs to see if there is an error with backups.
+
+Fix the errors.
+
+Try to delete some logs or other and restart the process.
+
+
+It should be fine.