Added info to gemspec.

Added instructions on running conversion with stylesheet to README.md

Author: RayOffiah

README.md

@@ -113,6 +113,14 @@ The callout attaches a class called `external-callout-block` to each source list
 
 The extension also adds a class called `external-callout-list` to the list of definitions at the bottom of the source block. (There's probably no need to adjust the styling for this.)
 
+Then to convert a document with a stylesheet, use something like this:
+
+```ruby
+Asciidoctor.convert_file File.join(File.dirname(__FILE__), 'sample.adoc'), 
+                         safe: :unsafe, backend: :html5,
+                         attributes: {'stylesheet' => './callout.css'}
+```
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

asciidoctor-external-callout.gemspec

@@ -9,7 +9,8 @@ Gem::Specification.new do |spec|
   spec.email         = ["clogs-wrench-0z@icloud.com"]
 
   spec.summary       = "Asciidoc extension for adding callouts without marking up the source listing block."
-  # spec.description   = "TODO: Write a longer description or delete this line."
+  spec.description   = "If you can't add callout markers to your source listing" \
+ "(if you need to keep a shell script runnable for example), then use this."
   spec.homepage      = "https://github.com/RayOffiah/asciidoctor-external-callout-ruby"
   spec.license       = "MIT"
   spec.required_ruby_version = Gem::Requirement.new(">= 2.3.0")