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/tvr/README.md

@@ -39,11 +39,19 @@ Mode may be a value from 0 to 12.
 
 ## Alternate code:
 
-The author provided us a spoiler version that might be of interest to some.
+
+### 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 without looking at the Alternate code.
+
+If you get stuck, come back and look at the Alternate code.
 
 
 ### Alternate build:
 
+The author provided us a less obfuscated version that might be of interest to some.
+
 ``` <!---sh-->
     make alt
 ```

1994/tvr/index.html

@@ -416,8 +416,12 @@ code</a> below.</p>
 <pre><code>    ./try.color.sh              # for colour displays
     ./try.bw.sh                 # for Black &amp; White displays</code></pre>
 <h2 id="alternate-code">Alternate code:</h2>
-<p>The author provided us a spoiler version that might be of interest to some.</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 without looking at the Alternate code.</p>
+<p>If you get stuck, come back and look at the Alternate code.</p>
 <h3 id="alternate-build">Alternate build:</h3>
+<p>The author provided us a less obfuscated version that might be of interest to some.</p>
 <pre><code>    make alt</code></pre>
 <h3 id="alternate-use">Alternate use:</h3>
 <pre><code>    ./tvr.alt altmode screensize/2 &lt; colormapfile</code></pre>