message: doc: annotate migration since version
  It tells us which migrations will run from a specific version.
diff: @@ -21,11 +21,11 @@ impl Migrate {
  pub fn new<P: Into<PathBuf>>(path: P) -> Self {
  let mut migrations = Migrations::default();
  migrations.add_migration(Box::new(DefaultMigration::new(INIT_DB_VERSION)));
  - migrations.add_migration(Box::new(migrations::ChangeMoleculeTableToStruct));
  - migrations.add_migration(Box::new(migrations::CellMigration));
  - migrations.add_migration(Box::new(migrations::AddNumberHashMapping));
  - migrations.add_migration(Box::new(migrations::AddExtraDataHash));
  - migrations.add_migration(Box::new(migrations::AddBlockExtensionColumnFamily));
  + migrations.add_migration(Box::new(migrations::ChangeMoleculeTableToStruct)); // since v0.35.0
  + migrations.add_migration(Box::new(migrations::CellMigration)); // since v0.37.0
  + migrations.add_migration(Box::new(migrations::AddNumberHashMapping)); // since v0.40.0
  + migrations.add_migration(Box::new(migrations::AddExtraDataHash)); // since v0.43.0
  + migrations.add_migration(Box::new(migrations::AddBlockExtensionColumnFamily)); // since v0.100.0
  Migrate {
  migrations,
  