Primer is not listed in github pages supported themes and wrong version in README

[agnostic-apollo]

The primer theme is not listed in the list of supported github pages themes, even though it works.

https://pages.github.com/themes

Also the version v0.2.0 listed in README is wrong and should be v0.6.0 since it generates the following error, also notified by someone else at #58 (comment). The version doesn't exist in releases either so users may get confused with the error.

Generating... 
      Theme: pages-themes/primer@v0.2.0
Theme source: /tmp/jekyll-remote-theme-20220623-2884100-8kxo2y
Remote Theme: Using theme pages-themes/primer
Remote Theme: Downloading https://codeload.github.com/pages-themes/primer/zip/v0.2.0 to /tmp/jekyll-remote-theme-20220623-2884100-4y1sar.zip
jekyll 3.9.2 | Error:  404 - Not Found - Loading URL: https://codeload.github.com/pages-themes/primer/zip/v0.2.0