Added script to install ubuntu20 i3 dependencies.

i3/install-ubuntu20-i3-deps

+#!/bin/bash
+apt install \
+meson \
+libstartup-notification0-dev \
+libxcb-xkb-dev \
+libstartup-notification0-dev \
+libxcb-xinerama0-dev \
+libxcb-randr0-dev \
+libxcb-shape0-dev \
+libxcb-util-dev \
+libxcb-cursor-dev \
+libxcb-keysyms1-dev \
+libxcb-icccm4-dev \
+libxcb-xrm-dev \
+libxkbcommon-dev \
+libxkbcommon-x11-dev \
+libyajl-dev \
+libpcre3-dev \
+libcairo2-dev \
+librust-pangocairo-dev \
+libev-dev