Document the availability attribute

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@152531 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index 296a3f5..2eb66d5 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -536,7 +536,7 @@
 /// version-arg:
 ///   'introduced' '=' version
 ///   'deprecated' '=' version
-///   'removed' = version
+///   'obsoleted' = version
 ///   'unavailable'
 /// opt-message:
 ///   'message' '=' <string>