Added pg_dump_suffix example inside role docs

roles/backup/README.md

@@ -75,7 +75,11 @@ It is also possible to tie the lifetime of the backup files to that of the AWXBa
 clean_backup_on_delete: true
 ```
 
-To customize the pg_dump command that will be executed on a backup use the `pg_dump_suffix` variable. This variable will append your provided pg_dump parameters to the end of the 'standard' command.
+To customize the pg_dump command that will be executed on a backup use the `pg_dump_suffix` variable. This variable will append your provided pg_dump parameters to the end of the 'standard' command. For example to exclude the data from 'main_jobevent' and 'main_job' to decrease the size of the backup use:
+
+```
+pg_dump_suffix: "--exclude-table-data 'main_jobevent*' --exclude-table-data 'main_job'"
+```
 
 Testing
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