apple: generate.sh: add a script to generate xcodeproj

The script explains how to generate the xcode project and will generate
a folder containing the project at the current working directory where
it has been used.

extras/package/apple/generate.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env sh
+
+SCRIPTDIR="$(cd "$(dirname "$0")" || exit 1; pwd)"
+VLC_SRC_DIR="$(cd "${SCRIPTDIR}/../../../" || exit 1; pwd)"
+PROJECTDIR="$(pwd)/xcodeproj/"
+
+export VLC_SRC_DIR
+mkdir -p "${PROJECTDIR}" && cd "${PROJECTDIR}" || exit 1
+
+xcodegen generate --project . --spec "${VLC_SRC_DIR}/extras/package/apple/xcodegen.yml" --project-root .