style tweaks for Guide addition

pkgs/racket-doc/scribblings/guide/io.scrbl

@@ -410,25 +410,21 @@ instead of the original byte stream.
   (interaction-eval #:eval port-eval (require racket/port racket/string)))
 
 For these examples, say you have two files in the same directory as
-your program.
-
-@filepath{oneline.txt} contains
+your program, @filepath{oneline.txt} and @filepath{manylines.txt}.
 
+@filebox["oneline.txt"]{
 @verbatim[#:indent 1]{
 I am one line, but there is an empty line after this one.
 
-}
-
-and
-
-@filepath{manylines.txt} contains
+}}
 
+@filebox["manylines.txt"]{
 @verbatim[#:indent 1]{
 I am
 a message
 split over a few lines.
 
-}
+}}
 
 If you have a file that is quite small, you can get
 away with reading in the file as a string:
@@ -466,9 +462,9 @@ any extraneous whitespace at the very beginning and very end of our file.
 (Lots of formatters out there insist that text files end with a single
 blank line).
 
-See also: @racket[read-line] if your file has one line of text.
+See also @racket[read-line] if your file has one line of text.
 
-If instead you want to process individual lines of a file, then you can
+If, instead, you want to process individual lines of a file, then you can
 use @racket[for] with @racket[in-lines]:
 
 @interaction[