Some of the quick start instructions need updating

[LTLA]

(Part of openjournals/joss-reviews#6617)

The Hello World example requires the submodules in third-party to be fetched. This is not done automatically on the initial git clone, at least not on my version of Git.

The header file names in Base tools are not correct (.h instead of .hpp).

And unrelated, but the title here has a typo ("Empirica's").

[mmore500]

Thanks for bringing these issues to our attention!

Just opened #514 with fixes for the three issues mentioned. When it merges, this issue will close. However, feel free to re-open if you find more lint or the issues are not adequately addressed 👍

[mmore500]

Closed by #514