Add upgrade guide

Upgrade-Invidious.md

@@ -0,0 +1,25 @@
+## Invidious releases are based on tags. You can use them if you want to be sure your instance is stable.
+
+#### With release tags
+```bash
+$ sudo -i -u invidious
+$ cd invidious
+$ git pull
+$ latestVersion=$(git describe --tags `git rev-list --tags --max-count=1`)
+$ git checkout $latestVersion
+$ shards
+$ crystal build src/invidious.cr --release
+$ exit
+$ sudo systemctl restart invidious.service
+```
+
+#### With master branch
+```bash
+$ sudo -i -u invidious
+$ cd invidious
+$ git pull
+$ shards
+$ crystal build src/invidious.cr --release
+$ exit
+$ sudo systemctl restart invidious.service
+```