.bazelrc: allow specifying a .bazelrc.user

This enables users to add their own local setting overrides
such as defaulting to debug mode.

Change-Id: Ibb27678be9994653d93c9a6931c640ab84301c3f
Reviewed-on: https://review.monogon.dev/c/monogon/+/758
Tested-by: Jenkins CI
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
diff --git a/.gitignore b/.gitignore
index e0ab998..c25fcea 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 *swp
 .idea
 .ijwb
+.bazelrc.user