Spec: Clarify mc_cfg_to_dot output

specification.md

@@ -517,14 +517,15 @@ This is the main compiler executable, sometimes referred to as *driver*.
     usage: mc_cfg_to_dot [OPTIONS] <file>
 
     Utility for printing a control flow graph in the DOT format. The output
-    can be visualised using graphviz. Errors are reported on invalid inputs.
+    contains multiple connected graphs, one per function. The output can be
+    visualised using graphviz. Errors are reported on invalid inputs.
 
     Use '-' as input file to read from stdin.
 
     OPTIONS:
       -h, --help                display this help message
       -o, --output <out-file>   write the output to <out-file> (defaults to stdout)
-      -f, --function <name>     print the CFG of the given function (defaults to 'main')
+      -f, --function <name>     print the CFG of the given function
 
 ### `mc_asm`