[docs] add a short note on how to use OpenWrt for daily work, covering the use...

[docs] add a short note on how to use OpenWrt for daily work, covering the use of quilt inside of OpenWrt, updating kernel, packages and patches

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@16606 3c298f89-4303-0410-b956-a3cf2f4a3e73