Adjustments to the install process and documentation

[marteki]

This PR makes several changes to the installation process and documentation, in hopes of avoiding errors or helping folks troubleshoot for themselves.

Additions

• Update gitignore to keep out ./Gemfile.lock (so old files aren't retained by mistake)
• Update README with more specific direction in case folks run into the bundle install error

Changes

• Update package.json to properly escape the double quotes that are expected by parallelshell in the npm start command

Testing

• Try to pull down the repo and load the server, preferably from scratch. You should be able to successfully get all the way to loading the server at http://localhost:4000/.

Review

• @Scotchester
• @jimmynotjim

Checklist

• [x] Changes are limited to a single goal (no scope creep)
• [x] Code can be automatically merged (no conflicts)
• [x] Code follows the standards laid out in the front end playbook
• [x] Passes all existing automated tests
• [x] New functions include new tests
• [x] New functions are documented (with a description, list of inputs, and expected output)
• [x] Placeholder code is flagged
• [x] Visually tested in supported browsers and devices
• [x] Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)

[jimmynotjim]

I can dig it.