README.md: Update Ubuntu 18.04 build: Add sound
Sound missing when following build instructions in Ubuntu 18.04. See
@@ -96,7 +96,7 @@ sudo sh cmake-3.12.0-Linux-x86_64.sh --skip-license --prefix=/usr
run the following commands in the Terminal
```
-sudo apt-get install g++ git cmake libgtk-3-dev libglvnd-dev libglu1-mesa-dev freeglut3-dev -y
+sudo apt-get install g++ git cmake libgtk-3-dev libglvnd-dev libglu1-mesa-dev freeglut3-dev libasound2-dev -y
git clone --recursive https://github.com/nesbox/TIC-80 && cd TIC-80/build
cmake ..
make -j4
