Doc: Add Upgrade guide for v2.0.2 -> v2.1.0

docs/src/upgrade-guide.md

@@ -0,0 +1,33 @@
+Upgrade Guide
+---------------------
+
+This doc is about how you should do to upgrade specified version to next version.
+
+Generally, you should have no extra action to take if you use our docker version
+if we haven't written notes for it.
+
+How to get the current version:
+```
+git tag
+```
+The first line of output is our latest version of code.
+
+
+# v2.0.2 -> v2.1.0
+Main breaking changes:
+
++  Upgrade `django 1` to django `2.2 LTS`
+
+How to:
+
+If you use non-docker version, you should change your web-server config to add a new
+alias for `media file path` (where to store images).
+
+Please add following config to your nginx config in `server` block:
+```
+location /media {
+    alias /path/to/static/media;
+    expires max;
+    access_log off;
+}
+```

mkdocs.yml

@@ -20,6 +20,7 @@ nav:
   - Install with Docker: 'install-with-docker.md'
   - Development: 'development.md'
   - Plugin System: 'plugin-system.md'
+  - Upgrade Guide: 'upgrade-guide.md'
   - Docs: 'docs.md'
   - Passwords: 'passwords.md'
   - Assets: 'assets.md'