Add readme instructions for how to build

[JessicaMeixner-NOAA]

Add to the existing readme or add a seperate readme with quick instructions of how to set-up and build.

This should either include or point to a list of required modules/libraries and clear instructions on how to build.

[JessicaMeixner-NOAA]

Instructions for how to run tests would also be appreciated.

[JessicaMeixner-NOAA]

Okay - I think some of the information I was looking for is here: https://github.com/NOAA-EMC/WW4/blob/develop/tools/README.md

So maybe we just simply need a quick note in the main readme to reference this.

Additionally, we need to state that you should be in the top level directory for the https://github.com/NOAA-EMC/WW4/blob/develop/tools/README.md#manual-usage manual usage instructions.

[HendrikTolman-NOAA]

@JessicaMeixner-NOAA After our discussions on how to make the compile system as simple as possible as per our draft requests for Jules, dealing with issues #62, #63, and #64 simultaneously, I pushed the Jules changes to to https://github.com/HendrikTolman-NOAA/WW4_HLT/tree/FT-Cmake-only-compile-system . Please take a look if this is generally what you wanted before I create a PR. Note that the documentation is now in the top-end README file so I can deal with this in a single PR later. I would like to move it later to the quick-start wiki page, and would like your input on that too.