Clashing tlm/ include directory with SystemC's `tlm` header file

[derchr]

Hi, I ran into an issue when installing both SystemC and SCC into the same prefix location. When installing the library into a prefix, the generated tlm directory under include could clash with the tlm header file by SystemC. So SCC cannot be installed into the same prefix as SystemC.

CMake Error at build/src/sysc/cmake_install.cmake:85 (file):
  file INSTALL cannot make directory
  "/home/derek/Git/SystemC-Components/prefix/include/tlm": File exists.
Call Stack (most recent call first):
  build2/cmake_install.cmake:67 (include)

[eyck]

This is a know limitation. SCC follows the rule to map namespaces into directory hierarchy. As there are quite a few TLM2.0 related things they reside in the tlm namespace and therefore clash with the tlm header file. We will update the documentation/README accordingly