update readme

Author: khiga8

README.md

@@ -1,2 +1,35 @@
 # erblint-github
 Template style checking for GitHub's Ruby projects
+
+## Setup
+
+1. Update your `Gemfile` and run `bundle install`
+
+``` ruby
+gem "erb_lint", require: false
+gem "erblint-github"
+```
+
+2. Require the linters within the `.erb-linters` folder. This could be done by adding a file `.erb-linters/erblint-github.rb` with the following line.
+
+```ruby
+require "erblint-github/linters"
+```
+
+3. Update the `erb-lint.yml` to configure the rule.
+
+### .erb-lint.yml
+
+```yaml 
+---
+linters:
+  GitHub::Accessibility::NoRedundantImageAlt:
+    enabled: true
+```
+
+## Testing
+
+```
+bundle install
+bundle exec rake test
+```