Rewrite about from HAML to Markdown (#1047)

Signed-off-by: Takuya Noguchi <[email protected]>

source/localizable/about.en.html.md

@@ -0,0 +1,49 @@
+---
+title: About this site
+layout: two_column_layout
+---
+
+# About this Web site
+
+## Source code
+
+[https://github.com/rubygems/bundler-site](https://github.com/rubygems/bundler-site)
+
+## Architecture
+
+Middleman 4.4 is the core system of this Web site.
+A half of source code is located in `./source`,
+but the other half is located in [rubygems/rubygems/tree/master/bundler/lib/bundler/man"](https://github.com/rubygems/rubygems/tree/master/bundler/lib/bundler/man),
+which would be retrieved by executing `bundle exec rake man`.
+
+When the source code is merged to the default branch `master` on GitHub,
+[Deploy job on GitHub Actions](https://github.com/rubygems/bundler-site/blob/HEAD/.github/workflows/deploy.yml)
+would automatically build source (HTML, JS, CSS and font) and push them to GitHub Pages.
+Deploy status can be followed in
+[github-pages Deployment history](https://github.com/rubygems/bundler-site/deployments/activity_log?environment=github-pages).
+Custom domain is used to host `bundler.io` (see also
+[Managing a custom domain for your GitHub Pages site](https://docs.github.com/en/pages/configuring-a-custom-domain-for-your-github-pages-site/managing-a-custom-domain-for-your-github-pages-site#configuring-a-subdomain)).
+
+As seen above, you might sometimes take care about the difference in
+deploy methods between review apps and production. Unlike production
+mentioned above, review apps of this Web site rely on Heroku architecture,
+which run as middleman server.
+
+## Localization
+
+While
+[internationalization system was introduced in 2016](/blog/2016/07/10/bundler-1-13-and-redesigned-bundler-io.html),
+multilingualization is still ongoing.
+We welcome multilingualize more guides and other documentations.
+To get started, move some files existing in `/source`
+or create a file to `/source/localizable`
+to multiligualize
+files.
+
+## Becoming a maintainer of this Web site (namely `rubygems/bundler-site`)
+
+If you want to be an official maintainer, start by helping out.
+
+As a first step, we welcome you to create a few of pull requests to improve
+the Web site to [the repo](https://github.com/rubygems/bundler-site/pulls).
+Also new feature improvement proposals are welcome.