add backup postgres info to README

README.md

@@ -156,6 +156,15 @@ SELECT * FROM webapi.source_daimon;
 
 Check sources: http://localhost:8080/WebAPI/source/sources
 
+Make a backup of the database: 
+* in the pgAdmin interface, right click on ohdsi "Backup Globals", save the file
+* retrieve the backup file in the pgAdmin container
+* move the file to the postgres container to restore a backup
+* execute the following command: 
+```bash
+psql -U postgres -d ohdsi < OHDSI_BACKUP
+```
+
 #### Oracle
 
 (This script is handy to delete all tables in a schema:)