Ignore .DS_Store

Add .DS_Store to the .gitignore list. These are MacOS files that
contain file metadata, so they're nonessential to the repository
and should be ignored by common git operations like `status` and
`add`.

Change-Id: I61cf3c8d426289fc1fba87c67e0b3557ca4e42f9

.gitignore

diff --git a/.gitignore b/.gitignore
index d5ef32f..047373e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 tags
 cmbuild
+.DS_Store
 .cproject
 .idea
 .project