Suggest basic auth in minimal example

Gerrit releases since a few years require HTTP basic authentication
rather than Gertty's default of digest. Add it in the minimal config
example since it's often overlooked by users and the number of
Gerrit deployments where the default works is rapidly dwindling.

Change-Id: I3138197991ae5f50f3ac956bf905ce5e01a50e7c

examples/minimal-gertty.yaml

@@ -11,3 +11,5 @@ servers:
     # Set corresponding HTTP password in gerrit settings
     password: CHANGEME
     git-root: ~/git/
+    # Needed for Gerrit 2.16 and later
+    auth-type: basic