improve how markdown code language is commented

We added a space between the markdown triple code mark
and language that was enclosed in HTML comments.

So a line of the form:

````
```<!---c--->
````

became:

````
``` <!---c--->
````

This was done to **help** some code see that the HTML comment
string was not a markdown code specifier.   Not all code
understands this after this changed.  For example, `pandoc(1)`
still forms HTML classes of the form "&lt;!---c--&gt;"
when it encounters the above mentioned change.

We also fixed a problem with `2019/dogon/README.md` regarding
a markdown code block.

We also fixed a problem with `2020/yang/README.md` regarding
a markdown code block.

2001/coupard/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./coupard
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -52,7 +52,7 @@ that can do sound, as a lowest-denominator sound I/O interface.
 
 To listen to what the program says directly, invoke
 
-```<!---sh-->
+``` <!---sh-->
     ./coupard > /dev/audio
 ```
 
@@ -68,7 +68,7 @@ If you want to convert the audio output of the program into another audio
 format, you can pipe it to [SoX](https://en.wikipedia.org/wiki/SoX) for example
 (`sox` is the Swiss army knife of Unix audio tools). The command:
 
-```<!---sh-->
+``` <!---sh-->
     ./coupard | sox -c1 -r8000 -tub - -c2 -r44100 -twav test.wav
 ```