Squashed 'third_party/gflags/' content from commit f0523f1

Change-Id: I7b525481a9f3ec3e48e6656735d06432c25dc3b9
git-subtree-dir: third_party/gflags
git-subtree-split: f0523f14a93cbb46fff9b318508aa1c6923158c7
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..aa2072c
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,4 @@
+[submodule "doc"]
+	path = doc
+	url = https://github.com/gflags/gflags.git
+	branch = gh-pages