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

Change-Id: Ia30ee40f4724b625c13d2dccd5da15b31395c997
MultiPart: 23/28
PresubmitTest: none
diff --git a/.gitignore b/.gitignore
index ff04d8d..81fa255 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
+/.jiri
+#TODO(nlacasse): Get rid of .v23 below once v23->jiri transition is complete.
 go/bin
 go/pkg