add user follow feature

db/migrate/20220227175028_create_user_follows.rb

@@ -0,0 +1,10 @@
+class CreateUserFollows < ActiveRecord::Migration[7.0]
+  def change
+    create_table :user_follows do |t|
+      t.references :follower, references: :users, foreign_key: { to_table: :users }
+      t.references :followed, references: :users, foreign_key: { to_table: :users }
+
+      t.timestamps
+    end
+  end
+end