add notices to those who wish for a greater challenge

We add the following level-3 header to help people identify text
they may wish to skip if they wish for a greater challenge:

```
```

After that notice we add:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program via the source.

If you get stuck, come back and read below for additional hints and information.
```

And sometimes follow with:

```
```

Or sometimes follow with:

```
```

Where the alt code impacts a "greater challenge", we add instead:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program without looking at the Alternate code.

If you get stuck, come back and look at the Alternate code.
```

And where a given command impacts a "greater challenge", we add instead:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program without running the command below.

If you get stuck, come back and run the following command:
```

Perform `make www` to perform the above and test under macOS.

1991/davidguy/README.md

@@ -86,7 +86,16 @@ In other words, even if we took steps to present the algorithm clearly, (we
 haven't) the relation of the computation performed to the specification of what
 the program was supposed to do would still be hard to understand.
 
-### Quasi-spoiler on internals:
+
+### 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.
+
+If you get stuck, come back and read below for additional hints and information.
+
+
+### How this entry works:
 
 The program plays [Conway's Game of
 Life](https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life) in the root window's

1991/davidguy/index.html

@@ -458,7 +458,11 @@ In other words, even if we took steps to present the algorithm clearly, (we
 haven’t) the relation of the computation performed to the specification of what
 the program was supposed to do would still be hard to understand.</p></li>
 </ol>
-<h3 id="quasi-spoiler-on-internals">Quasi-spoiler on internals:</h3>
+<h3 id="notice-to-those-who-wish-for-a-greater-challenge">NOTICE to those who wish for a greater challenge</h3>
+<p><strong>If you want a greater challenge, don’t read any further</strong>:
+just try to understand the program via the source.</p>
+<p>If you get stuck, come back and read below for additional hints and information.</p>
+<h3 id="how-this-entry-works">How this entry works:</h3>
 <p>The program plays <a href="https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life">Conway’s Game of
 Life</a> in the root window’s
 background pixmap. It starts by setting the background to random