Schema syntax consistency

Author: mrotteveel

doc/sql.extensions/README.schemas.md

@@ -247,10 +247,10 @@ ALTER SCHEMA <schema name>
     <alter schema option>...
 
 <alter schema option> ::=
-    SET DEFAULT CHARACTER SET <character set name> |
-    SET DEFAULT SQL SECURITY {DEFINER | INVOKER} |
-    DROP DEFAULT CHARACTER SET |
-    DROP DEFAULT SQL SECURITY
+    SET DEFAULT CHARACTER SET <character set name>
+  | SET DEFAULT SQL SECURITY {DEFINER | INVOKER}
+  | DROP DEFAULT CHARACTER SET
+  | DROP DEFAULT SQL SECURITY
 ```
 
 ### DROP SCHEMA