Updates to 1993/cmills - alt code + bugs + format

The README.md file has been format/typo checked.

The alt version uses usleep(3) with a configurable time (at compile
time). This version is suggested first as it apparently goes too fast in
modern systems. I say apparently as it doesn't appear to work with
macOS. I don't know if it works in other platforms but it is in bugs.md,
that there is a problem.

bugs.md

@@ -999,6 +999,16 @@ not a misunderstanding).
 # 1993
 
 
+### STATUS: known bug - please help us fix
+### Source code: [1993/cmills/cmills.c](1993/cmills/cmills.c)
+### Information: [1993/cmills/README.md](1993/cmills/README.md)
+
+We are unsure if this is a problem with multiple platforms but in macOS at least
+the program appears to just shows a black screen.
+
+Can you fix it? We welcome your help.
+
+
 ## 1993 lmfjyh
 
 ### STATUS: INABIAF - please **DO NOT** fix