Create a doc for updating the CMS (#1076)

website/site/content/docs/update-the-cms-version.md

@@ -0,0 +1,26 @@
+---
+title: Update the CMS Version
+position: 60
+---
+
+# Update the CMS Version
+
+The update procedure for your CMS depends upon the method you used to install Netlify CMS.
+
+## Package Manager
+
+If you are using a package manager like Yarn or NPM, you will use their standard procedure to update. This is how both the Hugo and Gatsby starters are set up.
+
+## CDN
+
+If you are using the CMS through a CDN like Unpkg, then that depends on the version tag you are using. You can find the version tag you are using in the `/admin/index.html` file of your site.
+
+- (Recommended) If you use `^1.0.0`, the CMS will do all updates except major versions automatically.
+   - It will upgrade to `1.0.1`, `1.1.0`, `1.1.2`.
+   - It will not upgrade to `2.0.0` or higher.
+   - It will not upgrade to beta versions.
+
+- If you use `~1.0.0`, the CMS will do only patch updates automatically.
+   - It will upgrade `1.0.1`, `1.0.2`.
+   - It will not upgrade to `1.1.0` or higher.
+   - It will not upgrade beta versions.