docs(mysql): init (#157)

doc/mysql.md

@@ -1,6 +1,46 @@
 # MySQL
 
->[!warning] 🚧 WIP
+[MySQL](https://github.com/mysql/mysql-server) is a popular open-source relational database management system (RDBMS).
 
-Usage example:
-<https://github.com/juspay/services-flake/blob/main/nix/mysql/mysql_test.nix>
+{#start}
+
+## Getting started
+
+```nix
+# In `perSystem.process-compose.<name>`
+{
+  services.mysql."mysql1".enable = true;
+}
+```
+
+{#tips}
+
+## Tips & Tricks
+
+{#port}
+
+### Use a different port
+
+```nix
+{
+  services.mysql."mysql1" = {
+    enable = true;
+    settings.mysqld.port = 3307;
+  };
+}
+```
+
+{#schema}
+
+### Multiple `.sql` files for schema
+
+The `schema` can be a path to a single `.sql` file or a directory containing multiple `.sql` files.
+
+```nix
+{
+  services.mysql."mysql1" = {
+    enable = true;
+    initialDatabases = [{ name = "test_database"; schema = ./test_schemas; }];
+  };
+}
+```