examples: flesh out PFN readme

Show how to actually use the arguments it has.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146845 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/examples/PrintFunctionNames/README.txt b/examples/PrintFunctionNames/README.txt
index 4c284cd..23ab5f0 100644
--- a/examples/PrintFunctionNames/README.txt
+++ b/examples/PrintFunctionNames/README.txt
@@ -7,6 +7,10 @@
 --
 Linux:
 $ clang -cc1 -load ../../Debug+Asserts/lib/libPrintFunctionNames.so -plugin print-fns some-input-file.c
+$ clang -cc1 -load ../../Debug+Asserts/lib/libPrintFunctionNames.so -plugin print-fns -plugin-arg-print-fns help -plugin-arg-print-fns --example-argument some-input-file.c
+$ clang -cc1 -load ../../Debug+Asserts/lib/libPrintFunctionNames.so -plugin print-fns -plugin-arg-print-fns -an-error some-input-file.c
 
 Mac:
 $ clang -cc1 -load ../../Debug+Asserts/lib/libPrintFunctionNames.dylib -plugin print-fns some-input-file.c
+$ clang -cc1 -load ../../Debug+Asserts/lib/libPrintFunctionNames.dylib -plugin print-fns -plugin-arg-print-fns help -plugin-arg-print-fns --example-argument some-input-file.c
+$ clang -cc1 -load ../../Debug+Asserts/lib/libPrintFunctionNames.dylib -plugin print-fns -plugin-arg-print-fns -an-error some-input-file.c