Update documentation: Add WordPress plugin and theme directory link

[kspilarski]

For first time or beginner users who might not be familiar with the directory, adding the link to plugins https://wordpress.org/plugins/ and themes https://wordpress.org/themes/ can be helpful in searching for plugins and themes names to be added to the url. And also for downloading plugins and themes to be uploaded to the site.

Docs:

• https://wordpress.github.io/wordpress-playground/start-using/#try-a-block-a-theme-or-a-plugin
• https://wordpress.github.io/wordpress-playground/build-your-first-app/#showcase-a-plugin-or-theme-from-wordpress-directory
• https://wordpress.github.io/wordpress-playground/limitations/#access-the-plugins-themes-blocks-or-patterns-directories

[adamziel]

This would be helpful indeed! We're a small team trying to maintain focus so I can’t commit to any specific timeframe here – thank you for reporting the issue!