Added a reference to embed_macros is the migrations module docs.
Fixes
//! folder itself should have the structure `{version}_{migration_name}`. It is recommended that
//! you use the timestamp of creation for the version.
//!
+//! Migrations can either be run with the CLI or embedded into the compiled application
+//! and executed with code, for example right after establishing a database connection.
+//! For more information, consult the [`embed_migrations!`](../macro.embed_migrations.html) macro.
+//!
//! ## Example
//!
//! ```text
