Missing template "layout/theme.liquid"

When I upload the zip file to Shopify I get an error saying "zip does not contain a valid theme: missing template "layout/theme.liquid". How can i fix it?

The package you received from Themeforest has the following items:

• File "Milano_main_official.zip" is the main item that needed to be uploaded to your store to make the theme work correctly without missing template "layout/theme.liquid".

• Folder "Licensing" contains the required license files of Milano theme.

• Folder "Data Import" contains a .zip and a .json file of Milano's Pages, a .csv file of Milano's sample Products.

• Folder "Demo Preset" contains all the .zip files of all the Milano's homepages. These files is to upload Milano theme to your store.

Note*: Before upload Milano theme to your store, please unzip "Package_Milano_v1.x.x" first then upload the "Milano_main_official.zip" file to your Shopify.