Refined CONTRIBUTING.md formatting

[dellagustin]

Issues:

• git command line tips section was not formatting command line instructions as code (using backticks), while other sections were (Build Process), which looked inconsistent and also required escaping the chars < and > (it impairs readability of the non-rendered Markdown version)
• One of the instructions in section General flow , which is formatting command line instructions as code, was also escaping the < and >, which led to rendered text shown escaping, as <master branch location&gt

I formatted all command line instructions as code and unescaped the escaped chars that were already in text formatted as code.

[dellagustin]

Can someone merge please? I am not a committer.

[rrrutledge]

I am leaving it open for a few days in case anyone else has comment. If not, then I will merge it in. Already have a reminder set to do it.

[lenucksi]

Thanks, this is great. Let's get this in.