Add 1994/imc/try.sh + inclusion of unistd.h

The inclusion of unistd.h is for getpid(2). While not strictly necessary
(at least not observed) this type of thing can be a problem and in some
other entries a missing or incorrect prototype caused the entry to fail
(sometimes only some systems namely macOS). This was just noticed by
chance and I did it on a whim.

1994/imc/README.md

@@ -17,12 +17,7 @@ where `[NUMBER]` is an optional number. Default is 5.
 ## Try:
 
 ```sh
-./imc 3
-./imc 3
-./imc 4
-./imc 4
-./imc 6
-./imc 13
+./try.sh
 ```