Added some documentation

Author: CA Lewis

clang-tools-extra/docs/clang-tidy/checks/kokkos-ensure-kokkos-function.rst

@@ -3,4 +3,5 @@
 kokkos-ensure-kokkos-function
 =============================
 
-FIXME: Describe what patterns does the check detect and why. Give examples.
+This check ensures that the user has annotated functions called by Kokkos with 
+one of the KOKKOS_FUNCTION style annotations.

clang-tools-extra/test/clang-tidy/checkers/kokkos-ensure-kokkos-function.cpp

@@ -9,5 +9,4 @@ KOKKOS_FUNCTION void f(){foo();}
 // CHECK-MESSAGES: :[[@LINE-1]]:26: warning: function 'foo' called in 'f' is missing a KOKKOS_X_FUNCTION annotation [kokkos-ensure-kokkos-function]
 
 
-// FIXME: Add something that doesn't trigger the check here.
 KOKKOS_FUNCTION void awesome_f2(){legal();}