[ADD] add xml pretty print to VIM

[umiphos]

In order to have a XML pretty print we need to install a library and edit the vimrc

1. Install xmllint (en ubuntu se encuentra dentro de libxml2-utils)
2. Add this line to ~/.vimrc

:map <F5> : silent %!xmllint --encode UTF-8 --format - :bnext <CR>

With this we mapped the key F5 as default key for this action. Remember that this action edit the current document.