minor #7456 Update doctrine.rst (patie, javiereguiluz)

This PR was submitted for the 3.2 branch but it was merged into the 2.7 branch instead (closes #7456). Discussion ---------- Update doctrine.rst schema_filter option should be full regular Commits ------- 1ad7eef Expanded the explanation and updated the example 6f31645 Update doctrine.rst

Author: xabbuh

reference/configuration/doctrine.rst

@@ -21,9 +21,9 @@ Full Default Configuration
  some_custom_type:
  class: Acme\HelloBundle\MyCustomType
  commented: true
- # If enabled all tables not prefixed with sf2_ will be ignored by the schema
- # tool. This is for custom tables which should not be altered automatically.
- #schema_filter: ^sf2_
+ # If defined, all the tables whose names match this regular expression are ignored
+ # by the schema tool (in this example, any table name starting with `wp_`)
+ #schema_filter:  "/^wp_/"
 
  connections:
  # A collection of different named connections (e.g. default, conn2, etc)