Fix markdown in README.md (#1180)

Title was not being formatted correctly.
diff --git a/README.md b/README.md
index 4a65571..ae0236f 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-#gRPC-Go
+# gRPC-Go
 
 [![Build Status](https://travis-ci.org/grpc/grpc-go.svg)](https://travis-ci.org/grpc/grpc-go) [![GoDoc](https://godoc.org/google.golang.org/grpc?status.svg)](https://godoc.org/google.golang.org/grpc)