TBR: mojo.discovery: Add '/.jiri' to .gitignore in all repos.

Change-Id: I9cc757b5f6d5c39dc096cbdfa6658554132dc290
MultiPart: 14/28
PresubmitTest: none
diff --git a/.gitignore b/.gitignore
index b7e2fde..c2296ef 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,3 @@
+/.jiri
+#TODO(nlacasse): Get rid of .v23 below once v23->jiri transition is complete.
 /.v23
\ No newline at end of file