Add Alpine build dependencies in README (#9206)

README.md

@@ -152,6 +152,10 @@ For Arch users:
 
     sudo pacman -S base-devel libcurl-gnutls cmake libxxf86vm irrlicht libpng sqlite libogg libvorbis openal freetype2 jsoncpp gmp luajit leveldb ncurses
 
+For Alpine users:
+
+    sudo apk add build-base irrlicht-dev cmake bzip2-dev libpng-dev jpeg-dev libxxf86vm-dev mesa-dev sqlite-dev libogg-dev libvorbis-dev openal-soft-dev curl-dev freetype-dev zlib-dev gmp-dev jsoncpp-dev luajit-dev
+
 #### Download
 
 You can install Git for easily keeping your copy up to date.