Added a simple bash script to install git-extras as aliases on global

git config.

Some people (like me) would prefer not to install git-extras' binaries
into /usr/bin/local but rather use them as git aliases.
I've added this script to fit that purpose.

git update-extras, simply update the git-extras local copy by pulling.

config-git-alias.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+# from http://stackoverflow.com/questions/59895/can-a-bash-script-tell-what-directory-its-in
+SCRIPT_PATH="${BASH_SOURCE[0]}";
+if([ -h "${SCRIPT_PATH}" ]) then
+  while([ -h "${SCRIPT_PATH}" ]) do SCRIPT_PATH=`readlink "${SCRIPT_PATH}"`; done
+fi
+pushd . > /dev/null
+cd `dirname ${SCRIPT_PATH}` > /dev/null
+SCRIPT_PATH=`pwd`;
+
+
+# Add an alias for each git-* script
+for bin in $SCRIPT_PATH/bin/git-*; do
+  cmd=$(basename $bin | sed s#git-##g)
+  echo git $cmd
+  git config --global alias.$cmd "!$bin"
+done
+
+# Update git-extras by simply pulling from remote.
+git config --global alias.update-extras "!(cd $SCRIPT_PATH && git pull)"