sqlx-cli/README.md: document that `<command> --help` exists
@@ -16,6 +16,8 @@ in the current working directory.
`database` and `migrate` subcommands support only Postgres; MySQL and SQLite are TODO.
+For more details, run `sqlx <command> --help`.
+
```dotenv
# Postgres
DATABASE_URL=postgres://postgres@localhost/my_database
