doc: fix description of build dependencies for Alpine Linux

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/build/gcc.rst b/doc/build/gcc.rst
index 0e0d87a..b883cf7 100644
--- a/doc/build/gcc.rst
+++ b/doc/build/gcc.rst
@@ -59,7 +59,7 @@
 .. code-block:: bash
 
     apk add alpine-sdk bc bison dtc flex linux-headers ncurses-dev \
-      openssl-dev python3 py3-setuptools python3-dev sdl2
+      openssl-dev perl python3 py3-setuptools python3-dev sdl2-dev
 
 Prerequisites
 -------------