update readme

README.md

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 # jekyll-theme-isabelline
 
-README is being worked on in [a post](/README/)
+Simple clean mobile-friendly theme for long form note taking. Works for blogging too.
+
+## Features:
+
+* Compatible with Jekyll 4
+* Designed for long form writing
+* Reserved, classy, easy to read, minimalistic visual design
+* Semantic lightweight mobile first markup; special attention to markup of block quotes, asides, images, image galleries
+* Customizable color scheme
+
+## Installation
+
+Add this line to site's `Gemfile`: 
+
+```ruby
+gem "jekyll-theme-isabelline", "~> 0.1.0"
+```
+And add this line to your Jekyll site:
+
+```yaml
+theme: jekyll-theme-isabelline
+```
+
+And then execute:
+
+```sh
+ $ bundle
+```
+
+Or, install from CLI:
+
+```sh
+ $ gem install jekyll-theme-isabelline
+```