Add an installation section for the two themes - [`@frontity/mars-theme`](https://api.frontity.org/frontity-packages/themes-packages/frontity-mars-theme) and [`@frontity/twentytwenty-theme`](https://api.frontity.org/frontity-packages/themes-packages/frontity-twentytwenty-theme). This is to provide installation instructions for a theme not chosen to be installed at the time that `npx frontity create` was run. Similar to [this](https://api.frontity.org/frontity-packages/features-packages/wp-source#installation).
Add an installation section for the two themes -
@frontity/mars-themeand@frontity/twentytwenty-theme.This is to provide installation instructions for a theme not chosen to be installed at the time that
npx frontity createwas run.Similar to this.