Add guide to README

README.md

@@ -1,7 +1,27 @@
+### Preparation
+You *can* connect directly to the Invidious database.
+
+Only the following tables are used and must be kept:
+- `playlist_videos`
+- `playlists`
+- `session_ids`
+- `users`
+
+You can delete the other ones.
+
+For example, if you're exporting the database:
+```bash
+pg_dump -U kemal -t playlist_videos -t playlists -t session_ids -t users invidious -Fc -Z3 > invidious.sql
+```
+This saves 90% of storage compared to running pg_dump without args, in my case 432M -> 25M
+
+Then:
+```bash
+cat invidious.sql | pg_restore -U kemal -d invidious
+```
+
 ### Environment variables
-- `QUART_SECRET_KEY`
-- `DATABASE_URL`
-- `ALTERNATIVE_INSTANCE_URL`, defaults to `https://redirect.invidious.io`
+See the [.env.example](.env.example) file
 
 ### Health check
-A `/health` endpoint is provided that returns `OK`
+A `/health` endpoint is provided that always returns `OK`