Add a simple way to run grpc-java test inside emulated ARM64 docker container

diff --git a/.gitignore b/.gitignore
index d5693c8..afa204c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -35,3 +35,6 @@
 # Emacs
 *~
 \#*\#
+
+# ARM tests
+qemu-arm-static