Add script to install files in the dist tarball.

Add a check inside Meson to detect if we're building from a git clone
or a dist tarball.
(in thie later, don't generated INSTALL.in and git-version.h)

meson_dist_script.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+cp -f 'INSTALL' "${MESON_DIST_ROOT}"
+# rm -f "${MESON_DIST_ROOT}/INSTALL.in"
+
+cp 'git-version.h' "${MESON_DIST_ROOT}"