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.

2019/lynn/README.md

@@ -89,11 +89,19 @@ and shows GHC also accepts our subset of Haskell:
 
 #### Self-hosting compiler:
 
-To avoid spoiling this entry by revealing the original Haskell source, we
+To avoid revealing the original Haskell source, we
 instead provide [hint.hs](%%REPO_URL%%/2019/lynn/hint.hs), the output of a certain stage of the
 compiler when run on itself. This intermediate output is hopefully difficult to
 understand, yet is accepted by our compiler:
 
+
+### 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 running the command below.
+
+If you get stuck, come back and run the following command:
+
 ``` <!---sh-->
     (./prog < hint.hs ; cat prog.c) > hint.c
     make hint

2019/lynn/index.html

@@ -443,10 +443,14 @@ includes <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/
 and shows GHC also accepts our subset of Haskell:</p>
 <pre><code>    ghc ghcfib.hs</code></pre>
 <h4 id="self-hosting-compiler">Self-hosting compiler:</h4>
-<p>To avoid spoiling this entry by revealing the original Haskell source, we
+<p>To avoid revealing the original Haskell source, we
 instead provide <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/lynn/hint.hs">hint.hs</a>, the output of a certain stage of the
 compiler when run on itself. This intermediate output is hopefully difficult to
 understand, yet is accepted by our compiler:</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 running the command below.</p>
+<p>If you get stuck, come back and run the following command:</p>
 <pre><code>    (./prog &lt; hint.hs ; cat prog.c) &gt; hint.c
     make hint
     ./hint</code></pre>