Small doc about CMake.

[stalkerg]

I wrote small README.cmake but my English is really poor and we must improve that.
In this document we must write about basic features of CMake and main differences between CMake and autotools+gnumake.

@markir9 can you help me?

[stalkerg]

Some version I pused to hackers.

Looks good. I'd recommend at line 17 to explicitly mention that you create a build dir e.g:

mkdir build
cd build
cmake ..

I note you do mention this at line 187, but for those people that jump straight in before reading to the end, being extra clear could be nice.