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.

1990/pjr/README.md

@@ -55,7 +55,15 @@ By use of pointers to functions returning a struct of pointers
 to functions!
 
 
-### Spoiler:
+### 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.
+
+
+### What this entry does:
 
 This program prints out the string:
 

1990/pjr/index.html

@@ -425,7 +425,11 @@ well.</p>
 it is done?</p>
 <p>By use of pointers to functions returning a struct of pointers
 to functions!</p>
-<h3 id="spoiler">Spoiler:</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="what-this-entry-does">What this entry does:</h3>
 <p>This program prints out the string:</p>
 <blockquote>
 <p>the quick brown fox jumped over the lazy dog</p>