docs: document changes don't mention the old keys

while the old way of declaring the keys is still available it is no longer documented

this should encourage new users to use the new, netrc-compatible way

docs/usage.rst

@@ -375,6 +375,9 @@ branch
 path
   Only commits containing this file path will be returned.
 
+host
+  Hostname for self-hosted GitHub instance.
+
 use_latest_release
   Set this to ``true`` to check for the latest release on GitHub.
 
@@ -415,7 +418,8 @@ An authorization token may be needed in order to use ``use_latest_tag``,
 
 To set an authorization token, you can set:
 
-- a key named ``github`` in the keyfile
+- an entry in your ``netrc`` file for the host
+- an entry in the keyfile for the host (e.g. ``github.com``)
 - the token option
 
 This source supports :ref:`list options` when ``use_max_tag`` is set.
@@ -447,7 +451,8 @@ token
 
 To set an authorization token, you can set:
 
-- a key named ``gitea_{host}`` in the keyfile, where ``host`` is all-lowercased host name
+- an entry in your ``netrc`` file for the host
+- an entry in the keyfile for the host (e.g. ``gitea.com``)
 - the token option
 
 This source supports :ref:`list options` when ``use_max_tag`` is set.
@@ -520,7 +525,8 @@ token
 
 To set an authorization token, you can set:
 
-- a key named ``gitlab_{host}`` in the keyfile, where ``host`` is all-lowercased host name
+- an entry in your ``netrc`` file for the host
+- an entry in the keyfile for the host (e.g. ``gitlab.com``)
 - the token option
 
 This source supports :ref:`list options` when ``use_max_tag`` is set.