[Documentation]Add Gentoo installation guide to README.md

[spixi]

Unlike the other Pidgin plugins, the lurch package for Gentoo does not start with x11-plugins/purple-. It can be fetched with the command

emerge x11-plugins/lurch

This could be added to the README.md file.

The following dependencies are automatically pulled by Gentoos package manager portage.

• dev-db/sqlite
• dev-libs/glib
• dev-libs/libgcrypt
• dev-libs/libxml2
• dev-libs/mxml
• net-libs/libaxc

[gkdr]

hi, and thanks for your input. i'll definitely consider it, i wanted to rewrite the whole readme soon anyway :slightly_smiling_face: