Ref dev/core#86

Also:

- Clarify that PRs don't need to have associated tickets
- Clean up some language here and there

Add health warning about running Docker on OSX

There are usually a few branches to choose from when picking a base-branch.
This breaks out a table to differentiate them.

Added documentation on Michael McAndrews docker container.

If I disagree with using the "NFC" label, I'd like to be able to quickly
reference a link that explains the rationale and provides examples.

This makes it easier to reference these things from other pages.

Tim and I added these instructions to amp (and improved them) so now
it's better to remove them here.

Replace 'Wordpress' with 'WordPress' to use correct camel casing according to the WordPress Wordmark and Trademark

Just spotted a typo in my previous change.  That 'v' should have been an 'h'.

The command `which civibuild` returns nothing even if the path is set correctly.

As noted earlier in the doc: "We strongly recommend using Apache as your
webserver because support for nginx is limited." So...  it doesn't make much
sense to give broken/incomplete instructions for something we say you
shouldn't do.  :)

Add in help message about troubleshooting where you cannot login to buildkit build because rewrite mod isn't enabled

Use more consistent capitalization and typography

Add `karma` and `upgrade`. Reorder alphabetically.