doc: actualise guide on how to make contributions

[sergeyklay]

Hi,

It's is an attempt to update information on how to make contributions. This patch makes the following changes:

• Replace the reference to the e2e directory with examples. The e2e directory has been deleted here chore: removed some files and moved a few things around #144
• Reformatted the file a bit to get rid of the horizontal scrolling
• Removed mention of Travis, which apparently has not been used by project for a very long time
• Replaced the broken links to the guides with others that will probably last longer
• Updated the Python versions of the pyenv examples

[sergeyklay]

@YOU54F @matthewbalvanz-wf Could you please take a look

[elliottmurray]

@sergeyklay Thanks!