Update documentation and Dockerfile to reflect necessary packages needed for Penthouse

Author: michael-misshore

README.md

@@ -2,19 +2,29 @@
 
 Only load the CSS you need for the initial viewport in Rails!
 
-This gem give you the ability to load only the CSS you *need* on an initial page view. This gives you blazin' fast rending as there's no initial network call to grab your application's CSS.
+This gem gives you the ability to load only the CSS you *need* on an initial page view. This gives you blazin' fast rending as there's no initial network call to grab your application's CSS.
 
 This gem assumes that you'll load the rest of the CSS asyncronously. At the moment, the suggested way is to use the [loadcss-rails](https://github.com/michael-misshore/loadcss-rails) gem.
 
 This gem uses [Penthouse](https://github.com/pocketjoso/penthouse) to generate the critical CSS.
 
-## Upgrading to the Latest Release
+## Dependency Requirements for / Upgrading to the Latest Release
 
-Upgrade instructions from each version are included below.
+### For 1.0.0 or later
+To maintain the latest version of Penthouse, this gem depends on NodeJS and NVM to be installed on the system.
+
+### For 2.0.0 or later
+This gem may require additional packages to be installed to run Chrome headless. Per the Penthouse documentation, this may be all you need:
+
+```
+sudo apt-get install libnss3
+```
+
+However, more packages may need to be installed depending on your OS distribution which can be found via [this answer](https://github.com/GoogleChrome/puppeteer/issues/404#issuecomment-323555784)
 
 ## Installation
 
-Add `critical-path-css-rails` to your Gemfile:
+After reviewing the dependency requirements, add `critical-path-css-rails` to your Gemfile:
 
 ```
 gem 'critical-path-css-rails', '~> 2.3.0'
@@ -110,9 +120,6 @@ Careful use of these methods allows the developer to generate critical path CSS
 
 A user can use these methods to [dynamically generate critical path CSS](https://gist.github.com/taranda/1597e97ccf24c978b59aef9249666c77) without using the `rake critical_path_css:generate` rake task and without hardcoding the application's routes into `config/critical_path_css.yml`.  See [this Gist](https://gist.github.com/taranda/1597e97ccf24c978b59aef9249666c77) for an example of such an implementation.
 
-## Upgrading from version 0.X.X to 1.0.0 or later
-To maintain the latest version of Penthouse, this gem now depends on NodeJS and NVM to be installed on the system.
-
 ## Upgrading from a version earlier than 0.3.0
 
 The latest version of Critcal Path CSS Rails changes the functionality of the `generate` method.  In past versions,
@@ -124,10 +131,10 @@ Developers upgrading from versions prior to 0.3.0 will need to replace `Critical
 rails generate critical_path_css:install
 ```
 
-Answer 'Y' when prompted to overwrite `critical_path_css.rake`.  However, overwriting `critical_path_css.yml` is not necessary and not recommended.
+Answer 'Y' when prompted to overwrite `critical_path_css.rake`.  However, overwriting `critical_path_css.yml` is not recommend nor necessary.
 
 
-## Testing
+## Testing / Development
 
 This gem is to be tested inside of docker/docker-compose. [Combustion](https://github.com/pat/combustion), alongside rspec-rails and capybara, are the primary components for testing. To run the test, you'll need to have [Docker](https://docs.docker.com/engine/installation) installed. Once installed, run the following commands in the gem's root to build, run, and shell into the docker container.
 

docker/ruby/Dockerfile

@@ -4,6 +4,9 @@ FROM ruby:2.5.0
 RUN curl -sL https://deb.nodesource.com/setup_8.x | bash -
 RUN apt-get update && apt-get install -y build-essential libpq-dev nodejs npm
 
+# Install Penthouse JS Dependencies
+RUN apt-get install -y libpangocairo-1.0-0 libx11-xcb1 libxcomposite1 libxcursor1 libxdamage1 libxi6 libxtst6 libnss3 libcups2 libxss1 libxrandr2 libgconf2-4 libasound2 libatk1.0-0 libgtk-3-0
+
 RUN npm cache clean -f
 RUN npm install -g n
 RUN n 8.9.3