Merge pull request #10844 from vector-im/bwindels/document-disable_cu…

…stom_urls

document disable_custom_urls

docs/config.md

@@ -20,8 +20,8 @@ For a good example, see https://riot.im/develop/config.json.
      if `default_hs_url` is used.
    * The identity server is used for verifying third party identifiers like emails
      and phone numbers. It is not used to store your password or account information.
-     If not provided, the identity server defaults to vector.im. Currently the only 
-     two public identity servers are https://matrix.org and https://vector.im, however 
+     If not provided, the identity server defaults to vector.im. Currently the only
+     two public identity servers are https://matrix.org and https://vector.im, however
      in future identity servers will be decentralised. In the future it will be possible
      to disable the identity server functionality.
    * Riot will fail to load if a mix of `default_server_config`, `default_server_name`, or
@@ -80,6 +80,8 @@ For a good example, see https://riot.im/develop/config.json.
 1. `defaultCountryCode`: The ISO 3166 alpha2 country code to use when showing
    country selectors, like the phone number input on the registration page.
    Defaults to `GB` if the given code is unknown or not provided.
+1. `disable_custom_urls`: disallow the user to change the
+   default homeserver when signing up or logging in.
 
 Note that `index.html` also has an og:image meta tag that is set to an image
 hosted on riot.im. This is the image used if links to your copy of Riot