message: Making MPI optional in docs, removing spdlog dependency
diff: @@ -19,8 +19,7 @@ The following third party libraries (TPLs) are used by XACC:
  | CMake | Required | 2.8+ |
  | Boost | Required | 1.59.0+ |
  | CppMicroServices | Required | Master |
  -| spdlog | Required | N/A |
  -| MPI | Required | N/A |
  +| MPI | Optional | N/A |
  ## Fedora/CentOS/Redhat Build Instructions
  