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.

archive/historic/README.md

@@ -79,7 +79,7 @@ Machine](https://web.archive.org) as of [2022 Dec
 
 *HINT*: To uncompress a given bzip2 compressed tarball file, use:
 
-```<!---sh-->
+``` <!---sh-->
 tar -jxvf file.tar.bz2
 ```
 
@@ -88,7 +88,7 @@ where "_file.tar.bz2_" is the name of a file found in this directory.
 To uncompress all of the 2022 Dec 28 archive using the year based
 bzip2 compressed tarball files:
 
-```<!---sh-->
+``` <!---sh-->
 for year in 198{4,5,6,7,8,9} 199{0,1,2,3,4,5,6,8} 200{0,1,4,5,6} 201{1,2,3,4,5,8,9} 2020; do
     rm -rf "$year"
     tar -jxvf "archive-$year.tar.bz2"