Ignore VsChromium config file

I rely on VsChromium for code search in Chromium and in depot_tools, so
it is appropriate to ignore its configuration file in both places.

Change-Id: I4481d565e2271d86f69ceb98037b9ace908bdf44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2715832
Commit-Queue: Gavin Mak <gavinmak@google.com>
Auto-Submit: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Gavin Mak <gavinmak@google.com>

.gitignore

@@ -90,3 +90,6 @@ testing_support/google_appengine
 
 # Ignore git traces produced by git push on git-cl upload.
 /traces
+
+# Ignore VsChromium configuration file.
+/vs-chromium-project.txt