Explain website generation using jekyll

docs/_README.md

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+# BRouter Docs
+
+This documentation can be used to generate a static website using [jekyll](https://jekyllrb.com/).
+
+## Dependencies
+
+jekyll uses ruby and therefore installs dependencies using gem. It is recommended to use bundler to manage those dependencies.
+
+`bundle install` installs all dependencies. To update dependencies use `bundle update`.
+
+## Preview
+
+jekyll provides a built-in webserver which can be used for fast feedback during editing.
+
+`bundle exec jekyll serve`