Add Feature Preview documentation (#846)

Author: gtsiolis

src/docs/feature-preview.md

@@ -0,0 +1,25 @@
+# Feature Preview
+
+You can enable Feature Preview from the Settings. This will enable a beta preview of some of the latest functionalities and features that are being actively developed. Some of them are user-facing features while others take place in the backstage.
+
+You can disable Feature Preview at any time.
+
+If you have suggestions on how we can improve a feature, please provide feedback by [opening an issue](https://github.com/gitpod-io/gitpod/issues/new/choose).
+
+> Once you enable this, existing and new workspaces will automatically start with all beta features. Disabling this could make existing workspaces unstable. 
+
+## Root Access
+
+Root Access allows you to attain privileged control within a workspace and be able to run commands as root.
+
+This feature also enables Docker in your workspace. Run `sudo docker-up` to start a Docker daemon.
+
+## Default IDE
+
+Gitpod uses Theia as the default IDE. This setting allows you to choose between [Theia](https://github.com/eclipse-theia/theia) and [Code](https://github.com/microsoft/vscode) editors as well as provide a custom IDE image.
+
+You can choose between 3 options:
+
+- Theia
+- Code
+- Image

src/docs/menu.ts

@@ -107,6 +107,10 @@ export const MENU: MenuEntry[] = [
             ),
         ]
     ),
+    M(
+        "Feature Preview",
+        "feature-preview",
+    ),
     M(
         "Gitpod Self-Hosted",
         "self-hosted/latest/self-hosted",