herokuにデプロイ出来ないです。

Question

前提・実現したいこと

HTMLで作ったサイトをherokuにデプロイしたい

発生している問題・エラーメッセージ

git push heroku master　をしたら下のエラーが出ました。

remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> Building on the Heroku-20 stack
remote: -----> Determining which buildpack to use for this app
remote:  !     No default language could be detected for this app.
remote:                         HINT: This occurs when Heroku cannot detect the buildpack to use for this application automatically.
remote:                         See https://devcenter.heroku.com/articles/buildpacks
remote:
remote:  !     Push failed
remote: Verifying deploy...
remote:
remote: !       Push rejected to site-assetstore-boot.
remote:
To https://git.heroku.com/site-assetstore-boot.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/site-assetstore-boot.git'