Segfault1602

Fix cmake build on windows

1

CMake build was broken on windows due to M_E being undeclared. Fix is to define `_USE_MATH_DEFINES` on windows when building the library.

Add building instruction to readme

1

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...