Updates to 1984/decot wrt alt/orig code

Update formatting of the alt code (heading levels) and added subsections
for how to build and run (rather than having it all together).

Updated the historical remarks as well. It's important in this case to
refer to decot.orig.c and not decot.alt.c because the orig code is the
one that was submitted whereas the alt code is the modification the
judges made.

1984/decot/README.md

@@ -16,10 +16,19 @@ make all
 
 ### Alternate code:
 
-To try the original code that requires `-traditional-cpp`:
+This alternate code, the original, requires a compiler that supports
+`-traditional-cpp` or an old enough compiler. If you have such a compiler you
+can use this entry.
+
+#### To build:
 
 ```sh
 make alt
+```
+
+#### To run:
+
+```sh
 ./decot.alt
 ```
 
@@ -45,7 +54,8 @@ to:
 for(signal=0;*k *x * __FILE__ *i;) do {
 ```
 
-To see what we mean look at the [original source file](decot.orig.c).
+To see what we mean look at the [original source file](decot.orig.c). The
+[alternate code](decot.alt.c) is the version that we modified.
 
 
 ## Author's remarks: