Add Style Guide to Contributing Guildines

[roseg31]

Contributing guidelines should include or link to a style guide so that all contributors can help keep the code understandable and maintainable.

Some ideas for guidelines include:

• Keeping code line length at 80 chars or less
• Adding comments for all functions
• Commenting or flagging issues when broken code is found
• Naming conventions (e.g. camel case for function names and file names)
• Writing descriptive commit messages/pull requests

[roseg31]

Additional information: https://google.github.io/styleguide/jsguide.html

[subuash]

Committed at 939c7df