Fix html vs md files issue in 2020/ferguson1

The solution is that when referring to html files have in parentheses
text like 'foo.md' on GitHub though with a link.

...at least I believe this should solve the problem. Time might show
otherwise but we'll see.

2020/ferguson1/terminals.md

@@ -232,8 +232,8 @@ properly. Because that's what funny means in this context.
 It'd be nice if curses could detect hitting more than one arrow key at the
 same time so that diagonal directions would be possible but unfortunately it's
 not (`cat -v` confirms this). Even if I were to define four extra keys what
-would they be? And what about the head character? The [HACKING](HACKING.md) file has
-information on this.
+would they be? And what about the head character? The [HACKING.html][]
+([HACKING](HACKING.md) on GitHub) file has information on this.
 
 I also limit the terminal size to 10 lines/columns but most likely it would
 require the cheat modes to win and in any event allowing certain low values
@@ -255,7 +255,8 @@ from a quick test this holds even with a terminal that has a white background.
 There is a way to force the background to remain white though that's by way of
 monochrome (so no colours); I discuss that and another related terminal specific
 in the troubleshooting guide (there's another way but it would take me over the
-iocccsize; I talk about it in the [HACKING](HACKING.md) file).
+iocccsize; I talk about it in the [HACKING.html][] ([HACKING](HACKING.md) on
+GitHub) file).
 
 ## <a name="monochrome" href="#toc">Monochrome terminals</a>
 
@@ -363,6 +364,8 @@ Perhaps you only need to add the `return;` to `C()`. My guess is that's the case
 but I do not know for certain.
 
 
+[HACKING.md]: HACKING.md
+[HACKING.html]: HACKING.html
 [Linux keyboard and console HOWTO]: https://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO.html
 [Linux keyboard and console HOWTO section 4]: https://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-4.html
 [snake-colours.sh]: snake-colours.sh