add documentation about database [skip ci]

Author: JaneJeon

website/docs/2. Installation/2.3 Advanced.md

@@ -4,6 +4,16 @@ Before you deploy the Blink server, you need a Postgres and a Redis database. By
 
 Please see the `docker-compose.yml` of the repo to see a working setup running on docker-compose.
 
+:::warning
+MySQL is not currently supported as Blink relies on some PostgreSQL-specific features/isn't tested on MySQL. We hope to add MySQL support in the future, but for now, a recent-ish version of PostgreSQL is required.
+:::
+
+### Database Migrations
+
+For both the docker and bare metal installations, Blink will automatically run database migrations (see `AUTO_MIGRATE=1` in the `.env` for why it's doing so), so you don't need a "release" step or anything - just spin it up and you're good to go!
+
+If you'd like to manually run migrations and prevent Blink from running it before actually spinning up the server, please set the environment variable `AUTO_MIGRATE=0`.
+
 ## Deploying to Your Own Server
 
 A few commonalities to keep in mind no matter how you're running the Blink server (most of these are standard 12-factor app practices):
@@ -59,12 +69,6 @@ npm i -P && \
 
 Note that we only support node LTS versions, so if you're expecting difficulties, try using the LTS build.
 
-## Database Migrations
-
-For both the docker and bare metal installations, Blink will automatically run database migrations (see `AUTO_MIGRATE=1` in the `.env` for why it's doing so), so you don't need a "release" step or anything - just spin it up and you're good to go!
-
-If you'd like to manually run migrations and prevent Blink from running it before actually spinning up the server, please set the environment variable `AUTO_MIGRATE=0`.
-
 ## Advanced Analytics
 
 See [the Architecture page](/Introduction/1.3%20Architecture) for advanced edge/server access log-based analytics!