Describe config.cmake block purpose

Co-authored-by: Ryan Curtin <ryan@ratml.org>

CMake/CMakeExtras.cmake

@@ -2,7 +2,7 @@
 
 # Joins arguments and places the results in ${result_var}.
 function(join result_var)
-  set(result )
+  set(result)
   foreach (arg ${ARGN})
     set(result "${result}${arg}")
   endforeach ()
@@ -18,4 +18,4 @@ function(set_verbose)
   list(REMOVE_AT SET_VERBOSE_CACHE 0)
   join(doc ${SET_VERBOSE_CACHE})
   set(${SET_VERBOSE_UNPARSED_ARGUMENTS} CACHE ${type} ${doc})
-endfunction()
+endfunction()

src/mlpack/CMakeLists.txt

@@ -160,7 +160,7 @@ endif ()
 # recurse into methods/.  If not, this function is empty.
 post_markdown_setup()
 
-# Installing CMake Helper Files
+# Installing CMake Helper Files for mlpack-config.cmake
 
 include(${PROJECT_SOURCE_DIR}/CMake/CMakeExtras.cmake)