Many README.md files updated

Formatting and other notes. Many more need to be checked for this but I
wanted these changes out of the way of git status to try and clean my
working changes.

2004/arachnid/README.md

@@ -26,6 +26,12 @@ make
 ./arachnid arachnid.info
 ```
 
+and then try:
+
+```sh
+./arachnid arachnid.c
+```
+
 ## Judges' comments
 
 The fun part comes when you realize that the maze scrolls.  The overall