Include license file in output dir builds as well

Author: hwangsihu

build.sh

@@ -51,6 +51,7 @@ docker run --rm -i $TTY_ARG "${UIDARGS[@]}" -v "$PWD/ffbuild":/ffbuild -v "$BUIL
 if [[ -n "$FFBUILD_OUTPUT_DIR" ]]; then
     mkdir -p "$FFBUILD_OUTPUT_DIR"
     package_variant ffbuild/prefix "$FFBUILD_OUTPUT_DIR"
+    [[ -n "$LICENSE_FILE" ]] && cp "ffbuild/ffmpeg/$LICENSE_FILE" "$FFBUILD_OUTPUT_DIR/LICENSE.txt"
     rm -rf ffbuild
     exit 0
 fi