docs - update postgres (#30592) (#30607)

Co-authored-by: Natalie <nat@metabase.com>

docs/databases/connections/postgresql.md

@@ -113,7 +113,13 @@ In some databases, Metabase can unfold JSON columns into component fields to yie
 
 ### Additional JDBC connection string options
 
-You can append options to the connection string that Metabase uses to connect to your database.
+You can append options to the connection string that Metabase uses to connect to your database. Use the format:
+
+```
+options=-c%20key=value
+```
+
+PostgreSQL connection URIs expect [percent-encoding](https://developer.mozilla.org/en-US/docs/Glossary/Percent-encoding) for whitespaces and symbols.
 
 ### Re-run queries for simple explorations