docs: Update description of how files are selected for instrumentation

[AndrewFinlay]

So I've put together a draft to better explain how files are included for coverage in nyc.

Take a look and tell me what you think, it probably needs a few changes here or there but I think it will take out a little of the mystery in configuring nyc.

[coveralls]

Coverage remained the same at 96.639% when pulling 497b871 on AndrewFinlay:include-exclude-doc into b64d921 on istanbuljs:master.

[JaKXz]

This is amazing, thank you so much @AndrewFinlay! Some minor nits and suggestions for you.

Also I think we can save some CI cycles if you just put [skip ci] in your commit messages :)

Last thing, what do you think of doing newlines at the end of sentences rather than the arbitrary line length? I think it makes reviewing changes a bit easier since each line is a sentence but I know there's this (IMO strange) pattern in place - maybe there's a good reason for it I don't know but I'm not a fan personally...

[AndrewFinlay]

@JaKXz thanks for the review,

I'll add the [skip ci] in future, simply didn't know it existed.

The line endings are simply an artefact of how I work with my editor. I'll fix it up tomorrow

[JaKXz]

This is odd... the single newlines are being rendered as <br/>s... not sure why that's happening.

[coreyfarrell]

This is odd... the single newlines are being rendered as
s... not sure why that's happening.

@JaKXz where are you seeing this?

[JaKXz]

@coreyfarrell in the rich diff

[coreyfarrell]

Thanks for working on this @AndrewFinlay!