[mkgmap-dev] Commit r4582: document special tag with prefix mkgmap:from-node:

Version mkgmap-r4582 was committed by gerd on Sat, 19 Sep 2020 document special tag with prefix mkgmap:from-node: (Patch by Marc Cousin, modified) http://www.mkgmap.org.uk/websvn/revision.php?repname=mkgmap&rev=4582