Add a description for the PatchableFunction pass; NFC

llvm-svn: 266721
diff --git a/llvm/lib/CodeGen/PatchableFunction.cpp b/llvm/lib/CodeGen/PatchableFunction.cpp
index ca345df..6fd9954 100644
--- a/llvm/lib/CodeGen/PatchableFunction.cpp
+++ b/llvm/lib/CodeGen/PatchableFunction.cpp
@@ -67,4 +67,5 @@
 
 char PatchableFunction::ID = 0;
 char &llvm::PatchableFunctionID = PatchableFunction::ID;
-INITIALIZE_PASS(PatchableFunction, "patchable-function", "", false, false)
+INITIALIZE_PASS(PatchableFunction, "patchable-function",
+                "Implement the 'patchable-function' attribute", false, false)