Enhance readme for local build

[chheis]

Could we add?
For Ubunut Users install:
CMocka with:
sudo apt-get install libcmocka-dev

[nayakned]

@chheis The cmake build has been adapted to handle cmocka as a dependency and the Readme has been updated to reflect your feedback. Let me know if you think more changes are required before we close this issue. Thanks.