Add building instruction to readme

[Segfault1602]

Right now it looks like there is 3 ways to build libDaisy: Makefile, CMake and Visual Studio.

While I appreciate the diversity, it would be useful to know which build system is preferred and guaranteed to stay up-to-date, assuming the maintainers are not committing to support an arbitrary number of build systems.

[takumi-ogata]

Thank you for pointing this out.

Officially, we primarily support make and all new build-related features land there first. It is our recommended build tool in combination with VS code as an editor.

We believe CMake is fully up to date. But there are some things we're not 100% sure how to do from there, such as bootloader apps (which should be possible). CMake support has been largely built up by the community, and we think it's important to those using it.

Visual Studio support has fallen behind a few times (there should be a pretty old PR that catches it up). We could go either way on keeping that or removing it.

When we get a chance, we will add more details about this in the README.md and then close this issue.
We greatly appreciated your feedback.