Update git-lfs message

Author: akenmorris

CMakeLists.txt

@@ -12,7 +12,7 @@ SET(SHAPEWORKS_VERSION "${SHAPEWORKS_MAJOR_VERSION}.${SHAPEWORKS_MINOR_VERSION}.
 # First, check that files were checked out properly using git-lfs
 file(MD5 "${CMAKE_CURRENT_SOURCE_DIR}/Testing/data/icp_baseline.nrrd" HASH)
 if (NOT "${HASH}" STREQUAL "bb94438a695c749b264180019abbbb97")
-  message( FATAL_ERROR "MD5 hash of '${CMAKE_CURRENT_SOURCE_DIR}/Testing/data/icp_baseline.nrrd' is incorrect.  This most likely means that git-lfs was not installed when ShapeWorks was cloned." )
+  message( FATAL_ERROR "MD5 hash of '${CMAKE_CURRENT_SOURCE_DIR}/Testing/data/icp_baseline.nrrd' is incorrect.  This most likely means that git-lfs was not installed when ShapeWorks was cloned.  If you have downloaded a zip or tar.gz of the source, then it will be missing Git-LFS objects.  Please use git to clone ShapeWorks or download a source archive containing the Git-LFS objects under releases." )
 endif()
 
 set(CMAKE_CXX_STANDARD 17)             # available options are [98, 11, 14, 17. 20]