Add documentation generation test

Author: MaxDesiatov

test/Documentation/docc.swift

@@ -0,0 +1,8 @@
+// REQUIRES: OS=macosx
+
+// RUN: %empty-directory(%t)
+// RUN: xcrun docc convert --output-path %t --ide-console-output --allow-arbitrary-catalog-directories $(dirname %utils)/docs
+
+// the generated bundle should be at least as big as the source directory
+// RUN: test $(du -c %t | tail -1 | awk '{ print $1 }') -gt $(du -c $(dirname %utils)/docs | tail -1 | awk '{ print $1 }') && echo success
+// CHECK: success