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.

1994/schnitzi/README.md

@@ -83,6 +83,14 @@ You might also wish to redirect the output to another file,
 compile it and compare how it works to the original code.
 
 
+### 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 is a program which takes any text file as input and 'flips'

1994/schnitzi/index.html

@@ -438,6 +438,10 @@ is different, but there is more than meets the <code>diff</code>’s eye. Can yo
 find out why?</p>
 <p>You might also wish to redirect the output to another file,
 compile it and compare how it works to the original code.</p>
+<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>
 <h2 id="authors-remarks">Author’s remarks:</h2>
 <p>This is a program which takes any text file as input and ‘flips’
 the input file along a diagonal running from the top left corner