Clarify CLI options

src/Main.hs

@@ -29,7 +29,7 @@ evaluateMode :: TricuArgs
 evaluateMode = Evaluate
   { file = def &= help "Input file path(s) for evaluation.\n \
       \ Defaults to stdin."
-      &= name "f"
+      &= name "f" &= typ "FILE"
     , form = FSL &= typ "FORM"
       &= help "Optional output form: (fsl|tree|ast|ternary|ascii).\n \
       \ Defaults to fsl \"Fork Stem Leaf\" form."
@@ -42,9 +42,9 @@ evaluateMode = Evaluate
 decodeMode :: TricuArgs
 decodeMode = Decode
   { file = def
-    &= help "Optional input file path(s) to attempt decoding.\n \
+    &= help "Optional input file path to attempt decoding.\n \
     \ Defaults to stdin."
-    &= name "f"
+    &= name "f" &= typ "FILE"
   }
   &= help "Decode a Tree Calculus value into a string representation."
   &= explicit