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.

1989/paul/README.md

@@ -41,9 +41,8 @@ better debugger or trace could easily be added.
 
 ## Judges' remarks:
 
-The author's comments is a detailed program explanation and spoiler.  If you
-want a real challenge, don't read any further and try to understand the program
-via the source.
+The author's comments is a detailed program explanation, if you wish to learn more about the obfuscation method used.
+
 
 ### Historical note:
 
@@ -55,6 +54,14 @@ However as this is no longer a problem the trailing `\` has been restored in all
 versions, both the original and the fixed for modern systems version.
 
 
+### 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.
+
+
 ## Author's remarks:
 
 This programs computes and prints Fibonacci numbers by