Moved the Upgrade Manuel out of FAQ (#3131)

### What problem does this PR solve?


### Type of change


- [x] Documentation Update

docs/guides/upgrade_ragflow.md

@@ -0,0 +1,43 @@
+---
+sidebar_position: 7
+slug: /upgrade_ragflow
+---
+
+# Upgrade RAGFlow
+
+You can upgrade RAGFlow to dev version or the latest version:
+
+- Dev versions are for developers and contributors. They are published on a nightly basis and may crash because they are not fully tested. We cannot guarantee their validity and you are at your own risk trying out latest, untested features.
+- The latest version refers to the most recent, officially published release. It is stable and works best with regular users.
+
+To upgrade RAGFlow to the dev version:
+
+Update the RAGFlow image and restart RAGFlow:
+
+1. Update **ragflow/docker/.env** as follows:
+
+   ```bash
+   RAGFLOW_IMAGE=infiniflow/ragflow:dev
+   ```
+
+2. Update RAGFlow image and restart RAGFlow:
+
+   ```bash
+   docker compose -f docker/docker-compose.yml pull
+   docker compose -f docker/docker-compose.yml up -d
+   ```
+
+To upgrade RAGFlow to the latest version:
+
+1. Update **ragflow/docker/.env** as follows:
+
+   ```bash
+   RAGFLOW_IMAGE=infiniflow/ragflow:latest
+   ```
+
+2. Update the RAGFlow image and restart RAGFlow:
+
+   ```bash
+   docker compose -f docker/docker-compose.yml pull
+   docker compose -f docker/docker-compose.yml up -d
+   ```