Restore the python auth instructions pending full conversion of mb.py

R=tikuta@chromium.org

Bug: 984869
Change-Id: I07a131c587e921a11ff1ac63a90831b794677a21
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437651
Commit-Queue: Fergal Daly <fergal@chromium.org>
Auto-Submit: Fergal Daly <fergal@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811582}

docs/workflow/debugging-with-swarming.md

@@ -152,10 +152,15 @@ for a platform you can't build for locally, does not yet exist.
 
 ## Authenticating
 
-You may need to log in to `https://isolateserver.appspot.com` to do this:
+You may need to log in to `https://chromium-swarm.appspot.com` to do this
+(for now you need to authenticate with python too,
+TODO(https://crbug.com/984869): remove this):
+
 
 ```
 $ tools/luci-go/isolate login
+$ python tools/swarming_client/auth.py login \
+      --service=https://chromium-swarm.appspot.com
 ```
 
 Use your google.com account for this.