Adding my new updating Mastodon guide (#367)

This is guide is for use with my recently merged Production Guide.

Running-Mastodon/Updating-Mastodon-Guide.md

@@ -0,0 +1,108 @@
+# Updating Mastodon
+
+This guide assumes you have the set up seen in the [Production Guide](./Production-Guide.md).
+
+## Read the release notes
+
+Please read the [release notes](https://github.com/tootsuite/mastodon/releases/) first.
+
+The release notes may contain special instructions that you may need to run for any given
+new Mastodon release.
+
+## Update the git repository
+After you are done reading the release notes, you will want to log in as the mastodon user
+and update the git repository.
+
+This is how you do that:
+
+```sh
+su - mastodon
+cd ~/live
+git pull
+git checkout $(git tag -l | sort -V | tail -n 1)
+```
+
+The above commands will update your copy of your git repository to the latest available
+tagged release.
+
+Always run tagged releases on production Mastodon instances. Never run the master branch
+on your production instance.
+
+You can always use `git status` to verify what tagged release your local 
+repository copy is at, for example:
+
+```sh
+mastodon@mastodon:~/live$ git status
+HEAD detached at v1.4.7
+nothing to commit, working directory clean
+```
+
+The above output indicates that my local repository copy is using the tagged release 'v1.4.7'
+of Mastodon.
+
+## Ruby and node.js dependency updates
+
+You may need to update Ruby and node.js upon updating to a new Mastodon release.
+The aforementioned release notes will mention if you need to do the rest of this section.
+
+This is how you update Ruby dependencies:
+```sh
+cd ~/live
+bundle install --deployment --without development test
+```
+
+This is how you update node.js dependencies:
+```sh
+cd ~/live
+yarn install --pure-lockfile
+```
+
+## Database schema updates
+
+Run a database schema every time you update to a new Mastodon release.
+It is safe to run this every time as it is a [no-op](https://en.wikipedia.org/wiki/NOP) if there are no database
+schema updates.
+
+This is how you run a database migration:
+```sh
+cd ~/live
+RAILS_ENV=production bundle exec rails db:migrate
+```
+
+## Pre-compiling updated assets
+
+You may need to pre-compile updated assets upon updating to a new Mastodon release.
+The aforementioned release notes will mention if you need to do the rest of this section.
+
+This is how you pre-compile assets:
+```sh
+cd ~/live
+RAILS_ENV=production bundle exec rails assets:precompile
+```
+
+A caveat:
+
+The assets pre-compiler ([Webpacker](https://github.com/rails/webpacker)) can take up 
+a non-trivial amount of resources, particularly RAM. If you find that your server is 
+running out of RAM when running the pre-compile, I recommend stopping the Mastodon services
+before starting the pre-compile.
+
+This is how you stop the Mastodon services (as root):
+```sh
+systemctl stop mastodon-*
+```
+
+## Restarting Mastodon services
+
+Mastodon runs in memory so you will need to restart it for any of the previous updates to take 
+effect.
+
+This is how you restart Mastodon services (as root):
+```sh
+systemctl restart mastodon-*.service
+```
+
+If you stopped the Mastodon services earlier as part of the assets pre-compile, replace
+the 'restart' with a 'start'.
+
+You now have an updated Mastodon instance. Keep up the good work!