manpage: add vertical space after bindkey examples

bindkey examples seem to be glued to their following descriptions.
This looks bad in the printable versions, so give it some space.

Alternatively we could possibly reverse the indentation and use
something like this:

bindkey -d

      Show all of the default key bindings.

but this is inconsistent with other examples.

src/doc/screen.1

@@ -1153,23 +1153,27 @@ Here are some examples of keyboard bindings:
 .nf
         bindkey \-d
 .fi
+.sp
 Show all of the default key bindings. The application mode entries
 are marked with [A].
 .sp
 .nf
         bindkey \-k k1 select 1
 .fi
+.sp
 Make the "F1" key switch to window one.
 .sp
 .nf
         bindkey \-t foo stuff barfoo
 .fi
+.sp
 Make "foo" an abbreviation of the word "barfoo". Timeout is disabled
 so that users can type slowly.
 .sp
 .nf
         bindkey "\e024" mapdefault
 .fi
+.sp
 This key-binding makes \*Q^T\*U an escape character for key-bindings. If
 you did the above \*Qstuff barfoo\*U binding, you can enter the word
 \*Qfoo\*U by typing \*Q^Tfoo\*U. If you want to insert a \*Q^T\*U
@@ -1178,6 +1182,7 @@ you have to press the key twice (i.e., escape the escape binding).
 .nf
         bindkey \-k F1 command
 .fi
+.sp
 Make the F11 (not F1!) key an alternative screen
 escape (besides ^A).
 .RE