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/burton/README.md

@@ -59,14 +59,24 @@ Compiles cleanly with:
 ### Description:
 
 Included is a test script, useful for the corner cases.  As in all good Unix
-programs, it is silent upon success; any output demonstrates an error.  Instead
-of checking correctness, the [check.sh](%%REPO_URL%%/2019/burton/check.sh) script can simply output the
-results:   (The Makefile contains the spoiler):
+programs, it is silent upon success; any output demonstrates an error.
+
+
+### 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-->
     out=cat ./check.sh ./prog
 ```
 
+Instead of checking correctness, the
+[check.sh](%%REPO_URL%%/2019/burton/check.sh) script can simply
+output the results:
+
 Interestingly, and a spoiler here: macOS and FreeBSD implement the common
 utility "correctly".  CentOS and Ubuntu both share a "flawed" utility that
 changes output format based upon input redirection or pipeline(!).  As well, the