gitconfig: Set xz archive format

.gitconfig

@@ -17,6 +17,8 @@ m = mergetool
 r = remote -v
 s = status -uno
 su = status -uno -u
+[tar "tar.xz"]
+command = xz -c
 [push]
 default = current
 
@@ -53,4 +55,4 @@ main = C !git checkout %(commit)
 main = ^D !git diff %(prompt) %(commit)
 [tig "color"]
 date = yellow default
-date = yellow default
+date = yellow default