Update Readme

[jurajsic]

There is some stuff missing or is outdated in readme, mainly:

• Mention that cmake (with minimal version) and a compiler supporting c++20 is needed to build mata.
• Mention that doxygen is an optional dependency to generate the documentation.
• Explain the dependencies (RE2, CUDD, simlib) - add links, what we use them for
• Installation is explained only for python binding, not for the main library.
• Is graphviz and graphviz-dev really needed for python binding? If yes, explain why.
• As mentioned in Set up code automatic coverage tests #142, update coverage explanation.
• Makefile in section Using the library is wrong, it links to simlib and re2, which is not needed (and will probably lead to error), there are missing include files from cudd... I would probably completely remove this makefile, and explain that if you want to use mata, use cmake, either by using it in a subdirectory with add_subdirectory or by finding the installed mata on system.