[build] Update the BUILD documentation for modern cmake usage. #1235
[build] Update the BUILD documentation for modern cmake usage. #1235

- Better explanation of CMake transitive include carried by using
target_link_libraries.

openMVG/openMVG,openMVG/openMVG,openMVG/openMVG,openMVG/openMVG,openMVG/openMVG