message: adding boost install instructions
diff: @@ -21,6 +21,18 @@ The following third party libraries (TPLs) are used by XACC:
  Note that you must have a C++14 compliant compiler.
  For GCC, this means version 6.1+, for Clang, this means 3.4+.
  +These dependencies are relatively easy to install on popular operating
  +systems. Any of the following commands will work (showing with and without MPI):
  +
  +.. code::
  +
  + $ (macosx) brew install boost
  + $ (macosx) brew install boost-mpi
  + $ (fedora) dnf install boost-devel
  + $ (fedora) dnf install boost-mpich-devel
  + $ (fedora) dnf install boost-openmpi-devel
  + $ (ubuntu) apt-get install libboost-all-dev # will install openmpi
  +
  Build XACC
  -----------
  