Bumped CMake requirement to 3.5, following agreement on ACTS-223
Since there was agreement on CMake 3.5+ as a new baseline for both ACTS and ACTSFW on JIRA, I propose to do the following...
- Bump the CMakeLists requirements of both projects early on, to quickly spot possible user-side issues
- Move my small how-to on using CVMFS cmake releases to this project.
Related to ACTS-234.