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.

2020/kurdyukov4/README.md

@@ -1,13 +1,13 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./prog text_file output_length context_length random_seed
 ```
 
@@ -17,7 +17,7 @@
 When running this, ask yourself why it gets progressively slower when the
 context length decreases:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -70,7 +70,7 @@ Now can you appreciate the award title a bit better?
 
 ### Building:
 
-```<!---sh-->
+``` <!---sh-->
     cc prog.c -o prog
 ```
 
@@ -79,7 +79,7 @@ Now can you appreciate the award title a bit better?
 This program generates random text from the provided dictionary using a Markov
 chain, outputting to `stdout`.
 
-```<!---sh-->
+``` <!---sh-->
     ./prog input.txt 2000 10 12345
 ```
 
@@ -110,7 +110,7 @@ You can try this with the inputs provided with
 [2019/mills](../../2019/mills/index.html) from the IOCCC entries.
 
 
-```<!---sh-->
+``` <!---sh-->
     $ ./prog Shakespeare.txt 2001 10 12345
 ```