Update README.markdown

$ pear install pear.netpirates.net/phpDox-0.5.0
Failed to download nikic/PHPParser within preferred state "stable", latest release is version 0.9.3, stability "beta", use "channel://nikic.github.com/pear/PHPParser-0.9.3" to install
theseer/phpDox requires package "nikic/PHPParser" (version >= 0.9.3)
No valid packages found
install failed