Merge pull request #1109 from ExpressionEngine/feature/email_as_username

Docs for member registration email_as_username parameter

Author: TomJaeger

docs/member/registration.md

@@ -31,6 +31,12 @@ Adds the datepicker to your date fields. Defaults to "yes".
 
 NOTE: **Note:** If you are manually constructing a date field, in order to apply the date picker you must include `rel="date-picker"`.
 
+
+### `email_as_username="yes"`
+    email_as_username="yes"
+
+When set to `yes`, if the username is not specified in the submitted form, the value of the submitted email will be automatically used as the username as well.  The username field is not required, but is optional, when this parameter is used.
+
 ### `error_handling="inline"`
     error_handling="inline"