[mkgmap-dev] Instructions to make contour maps

I spent a lot of time today trying to figure out the above and did not succeed. Would anyone be willing to produce a step by step guide on how to achieve it please? It took me a long time to find a server where I could download .hgt files and then I played with various combinations of options -- contours --dem-type=SRTM dem-path=dir_with_(compressed)_hgt_file(s) but I kept getting garbage I would really appreciate it. Thanks, Cliff