reduce the list of text extensions (remove .txt)

the .txt file should be kept as it is. we just want to support
a few number of file types html, erb, js, md, rb
doc + gitconfiguration doc (from #archlinuxvn)

Is there any way to compile the doc. from #archlinuxvn automatically
without manual checking out/ adding? (and to reduce the resource)
news: announce the project on ArchLinux, SaigonLug

Link:
. https://groups.google.com/group/archlinuxvn/browse_thread/thread/365396651fc80c51
. https://groups.google.com/group/saigonlug/browse_thread/thread/365396651fc80c51