add support for XML (flat open document format)

gardening-calendar.sh

@@ -55,7 +55,7 @@ RULE="$(realpath "${4}")" || exit_help 4 "Ruled page document not specified"
 for input in "${RULE}" "${TITLE}" "${CAL}"; do
     [ -e "${input}" ] || die -1 "File doesn't exist: '${input}'"
     ftype=$(file -b "${input}")
-    echo "${ftype}" | grep 'OpenDocument\|PDF' >/dev/null || die -1 "Unsupported file type: ${ftype}"
+    echo "${ftype}" | grep 'OpenDocument\|PDF\|XML' >/dev/null || die -1 "Unsupported file type: ${ftype}"
     FTYPES["${input}"]="${ftype}"
 done
 cat <<EOF >&2