Update documentation with contents by twrnh

content/en/admin/upgrading.md

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+---
+title: Upgrading to a new release
+menu:
+  docs:
+    weight: 70
+    parent: admin
+---
+
+{{< hint style="info" >}}
+When a new version of Mastodon comes out, it appears on the [GitHub releases page](https://github.com/tootsuite/mastodon/releases). Please mind that running unreleased code from the `master` branch, while possible, is not recommended.
+{{< /hint >}}
+
+Mastodon releases correspond to git tags. First, switch to the `mastodon` user:
+
+```bash
+su - mastodon
+```
+
+And navigate to the Mastodon root directory:
+
+Download the releases’s code, assuming that the version is called `v2.5.0`:
+
+```bash
+git fetch --tags
+git checkout v2.5.0
+```
+
+**The release page contains a changelog, and below it, upgrade instructions**. This is where you would execute them, for example, if the release mentions that you need to re-compile assets, you would execute:
+
+```bash
+RAILS_ENV=production bundle exec rails assets:precompile
+```
+
+After you have executed all special release-specific instructions, the last thing remaining is restarting Mastodon. _Usually_ the streaming API is not updated, and therefore does not require a restart. Restarting the streaming API can lead to an unusually high load on the server, so it is advised to avoid it if possible.
+
+Switch back to root:
+
+```bash
+exit
+```
+
+You would restart Sidekiq:
+
+```bash
+systemctl restart mastodon-sidekiq
+```
+
+And you would reload the web process to avoid downtime:
+
+```bash
+systemctl reload mastodon-web
+```
+
+**That’s all!** You’re running the new version of Mastodon now.
+