Add missing newline to code generation (#745)

We need to have a newline between the codegen comment and the start of
the generated docs because the markdown formatter will add it later.

hack/helm-reference-gen/main.go

@@ -115,7 +115,7 @@ func main() {
 	helmReferenceContents := string(helmReferenceBytes)
 
 	// Swap out the contents between the codegen markers.
-	startStr := "<!-- codegen: start -->\n"
+	startStr := "<!-- codegen: start -->\n\n"
 	endStr := "\n  <!-- codegen: end -->"
 	start := strings.Index(helmReferenceContents, startStr)
 	if start == -1 {