Allow user-specific `user.bazelrc` per "Best Practices for Bazel"

https://docs.bazel.build/versions/master/best-practices.html describes allowing a user-specific `user.bazelrc` in a workspace, but Bazel itself doesn't do this. This makes it a bit annoying to set flags every time.

Closes #10113.

PiperOrigin-RevId: 277718379
diff --git a/.bazelrc b/.bazelrc
index 1ad4a27..8153496 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -42,4 +42,5 @@
 # Alias
 build:remote --config=ubuntu1604_java8
 
-
+# User-specific .bazelrc
+try-import user.bazelrc