doc: Add note on upgrading into release notes and install.md

Closes #1652
Closes #2221

Author: nhooyr

ci/build/release-github-draft.sh

@@ -15,6 +15,8 @@ v$VERSION
 
 VS Code v$(vscode_version)
 
+See [upgrading](doc/install.md#upgrading) to upgrade.
+
 ## New Features
   - ⭐ Summarize new features here with references to issues
 

doc/install.md

@@ -2,6 +2,7 @@
 <!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
 # Install
 
+- [Upgrading](#upgrading)
 - [install.sh](#installsh)
   - [Flags](#flags)
   - [Detection Reference](#detection-reference)
@@ -19,6 +20,12 @@
 This document demonstrates how to install `code-server` on
 various distros and operating systems.
 
+## Upgrading
+
+When upgrading you can just install the new version over the old one. code-server
+maintains all user data in a separate directory so that it is preserved in between
+installations.
+
 ## install.sh
 
 We have a [script](../install.sh) to install code-server for Linux, macOS and FreeBSD.