Tests don't build; add doc

[willwray]

Please add a doc on how to build the tests.

A fresh git clone configures nicely from IDE or commandline,

> cmake -G Ninja -S . -B build

It magically downloads CPM, tts and eve, and then reports:

...
[cmake] -- [kyosu] - Setup for version 0.1.0
[cmake] -- [kyosu] - Building in Debug mode
[cmake] -- [kyosu] - Unit tests : ON (via KYOSU_BUILD_TEST)
[cmake] -- [kyosu] - Doxygen    : OFF (via KYOSU_BUILD_DOCUMENTATION)
[cmake] -- Configuring done (2.2s)
[cmake] -- Generating done (0.3s)
[cmake] -- Build files have been written to: /home/will/repos/kyosu/build

An attempt to build then does nothing:

> cmake --build build --target all
[0/2] Re-checking globbed directories...
ninja: no work to do.

CTest fails to find any exes, because none have been built.

How to build and run the tests?

[jfalcou]

Yeah, this should be

ninja kyosu-test

I will add doc but I'll also update copacabana cmake so that your command works out of the box