add: project menu list

db/migrate/20210317012035_create_project_units.rb

@@ -0,0 +1,10 @@
+class CreateProjectUnits < ActiveRecord::Migration[5.2]
+  def change
+    create_table :project_units do |t|
+      t.references :project 
+      t.integer :unit_type
+
+      t.timestamps
+    end
+  end
+end