Update gsubtreed docs with more details.

infra/services/gsubtreed/README.md

 # Gsubtreed
 
 #### (git subtree daemon)
 
 Gsubtreed is a daemon which mirrors subtrees from a large git repo to their
 own smaller repos. It is typically run for medium-term intervals (e.g. 10 min),
 restarting after every interval. While it's running it has a short (e.g. 5s)
 poll+process cycle for the repo that it's mirroring.
 
 ## Setup:
 
 1.  Push a file named `config.json` to the `refs/gsubtreed-config/main` ref of
     the repo you intend to mirror. Its contents is determined by
     [`GsubtreedConfigRef`][1]. You must at least set the `enabled_paths`
     portion.
     *   You should create a new line of history (e.g. `git checkout --orphan`)
         to avoid having unecessary extra files in this ref (as opposed to
         branching it off of another ref like `master`). Note that you'll
         probably also want to do a `git rm -rf` after you check out the orphan
         ref to clear the index+working copy.
+
+    ```sh
+    git checkout --orphan gsubtreed-config/main
+    git rm -rf *
+    vim config.json ## Edit the file
+    git commit -am 'Created gsubtreed config'
+    git push remote refs/gsubtreed-config/main
+    ```
+
 1.  (optional) If you have existing git mirrors (probably mirrored via git-svn),
     disable the mirroring service for them. If not, create the mirrors. By
     default if gsubtreed mirrors the path `bob` in `https://.../repo`, it will
     expect to find the mirror repo at `https://.../repo/bob`. You can change
     this with the `base_url` parameter in the config.
     *   If you do have existing mirrors, you will also need to bootstrap them.
         gsubtreed uses the mirror repos to store state about what it has already
         processed. It stores state as commit footers (e.g. `Cr-Mirrored-From`)
         The existing mirrors don't have this state so we have to cheat.
 
@@ skipping 20 matching lines @@
         this directly with the `git update-ref` command after fetching the
         existing notes from the mirror.
 
 1.  Once your mirrors are in a good state (either empty or primed with
     `extra_footers`), you should be able to run: `run.py
     infra.services.gsubtreed <repo url>` and it should Just Work.
 
 1.  At this point you should set up a new bot on the [infra cron waterfall][2]
     to run this on a regular interval.
 
+    * Request a new VM for the bot -
+      [sample ticket](http://crbug.com/626818) (internal)
+
+    * Use existing gsubtreed configs as templates in `master.cfg` and
+      `slaves.cfg` to set it up; remember to add the new bot to the
+      `Periodic` scheduler together with the other gsubtreed bots
+
+    * Push the appropriate credentials to the VM -
+      [see an example CL](http://go/chromerev/469017013) (internal).
+
 ## Usage:
 
     run.py infra.services.gsubtreed <repo_url>
 
 ## GsubtreedConfigRef fields
 
 *   `interval` *number*: The time in seconds between iterations of gsubtreed.
     Each iteration will fetch from the main repo, and try to push to all of the
     subtree repos.
 
@@ skipping 22 matching lines @@
     base_url was `https://example.com`, then it would mirror `path/to/foo` to
     `https://example.com/bar`, instead of `https://example.com/path/to/foo`.
 
 *   `path_extra_push` *{string: [string]}*: A dictionary mapping `enabled_path`
     to a list of full_git_repo_urls. Any time we find changes in the
     enabled_path, we'll also push those subtree commits to all the git repos in
     full_git_repo_urls.
 
 [1]: ./gsubtreed.py#32
 [2]: http://build.chromium.org/p/chromium.infra.cron