Documentation issue - README.md

[georgerapp]

Hi -

Appreciate your work to create this theme.

One error in README.md - the git command to add this theme to Hugo creates an error:

git submodule add https://github.com/gangjun06/SimpleIntro themes/SimpleIntro
fatal: unable to access 'https://github.com/gangjun06/SimpleIntro themes/SimpleIntro/': The requested URL returned error: 400
fatal: clone of 'https://github.com/gangjun06/SimpleIntro themes/SimpleIntro' into submodule path '[redacted]/SimpleIntro' failed

Suggest changing to this command, which succeeded:
git submodule add https://github.com/gangjun06/SimpleIntro