bump version to 0.6.0

[Evgeny Pogrebnyak]

The README.md lists pages-themes/primer@v0.2.0 and it results in error:

      Remote Theme: Downloading https://codeload.github.com/pages-themes/primer/zip/v0.2.0 to /tmp/jekyll-remote-theme-20220807-6-biq7rw.zip
github-pages 227 | Error:  404 - Not Found - Loading URL: https://codeload.github.com/pages-themes/primer/zip/v0.2.0