feat: add migration guide

docs/astro.config.mjs

@@ -42,6 +42,7 @@ export default defineConfig({
           label: "Admin",
           items: [
             { slug: "admin/quickstart" },
+            { slug: "admin/guides/migrating" },
             {
               label: "Guides",
               items: [

docs/src/content/docs/admin/guides/migrating.mdx

@@ -0,0 +1,48 @@
+---
+title: Migrating from v0.3.x
+description: A guide on how to migrate to v0.4.0 from v0.3.X
+---
+
+:::caution
+Because of the new manifest format and configuration, all your imported versions will be deleted.
+:::
+
+## Updating the `compose.yaml`
+
+To get started, simply update the tag in your `compose.yaml` to the tag you're using:
+
+```diff compose.yaml
+services:
+  postgres:
+    image: postgres:14-alpine
+    healthcheck:
+      test: pg_isready -d drop -U drop
+      interval: 30s
+      timeout: 60s
+      retries: 5
+      start_period: 10s
+    volumes:
+      - ./db:/var/lib/postgresql/data
+    environment:
+      - POSTGRES_PASSWORD=drop
+      - POSTGRES_USER=drop
+      - POSTGRES_DB=drop
+  drop:
+-    image: ghcr.io/drop-oss/drop:latest
++    image: ghcr.io/drop-oss/drop:v0.4.0-rc-1
+    depends_on:
+      postgres:
+        condition: service_healthy
+    ports:
+      - 3000:3000
+    volumes:
+      - ./library:/library
+      - ./data:/data
+    environment:
+      - DATABASE_URL=postgres://drop:drop@postgres:5432/drop
+      - EXTERNAL_URL=http://localhost:3000 # default, customise if accessing from another computer or behind a reverse proxy
+```
+
+## Re-importing all your versions
+
+Head to the admin library and re-import your versions one at a time. Optionally, you can use the new "Mass Import Tool", but keep in mind you can't configure many of the fancy new features with it.