Slight change in 'greater challenge' line

In the line in README.md and index.html files that said:

    ### NOTICE to those who wish for a greater challenge

I added a ':' at the end of the line.

There were some entries that had a link fix in the index.html file but I
only looked up through 1995/leo as those still have to have a 'look and
feel' check and it would just slow things down.

1995/leo/README.md

@@ -254,7 +254,7 @@ Special thanks:
 [isotopes](https://en.wikipedia.org/wiki/Isotope).
 
 
-### NOTICE to those who wish for a greater challenge
+### NOTICE to those who wish for a greater challenge:
 
 **If you want a greater challenge, don't read any further**:
 just try to understand the program via the source.
@@ -264,7 +264,7 @@ If you get stuck, come back and read below for additional hints and information.
 
 ### Secret switch
 
-See [secret.html[(secret.html) for a bit if secret switch information.
+See [secret.html](secret.html) if you wish to know the secret switch.
 
 
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