Add script to create .desktop file for Linux

For #208

resources/linux/create_desktop_file.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+set -e
+WORKING_DIR=`pwd`
+THIS_PATH=`readlink -f $0`
+cd `dirname ${THIS_PATH}`
+FULL_PATH=`pwd`
+cd ${WORKING_DIR}
+cat <<EOS > Mattermost.desktop
+[Desktop Entry]
+Name=Mattermost
+Comment=Mattermost Desktop application for Linux
+Exec="${FULL_PATH}/Mattermost"
+Terminal=false
+Type=Application
+Icon=${FULL_PATH}/icon.png
+EOS
+chmod +x Mattermost.desktop