docs: make the synopsis of --speller and 'set speller' more accurate

doc/nano.1

@@ -263,8 +263,8 @@ at the width of the screen minus \fInumber\fR columns, allowing the wrap
 point to vary along with the width of the screen if the screen is resized.
 The default value is \-8.
 .TP
-.BR \-s\ \fIprogram ", " \-\-speller= \fIprogram
+.B "\-s ""\fIprogram\fR [\fIarg\fR...]\fB""\fR, \fB\-\-speller=""\fIprogram\fR [\fIarg\fR...]\fB"""
-Use this alternative spell checker command.
+Use this alternative command to perform spell checking.
 .TP
 .BR \-t ", " \-\-tempfile
 Save a changed buffer without prompting (when exiting with \fB^X\fR).

doc/nano.texi

@@ -388,8 +388,8 @@ point to vary along with the width of the screen if the screen is resized.
 The default value is @t{-8}.
 
 @anchor{@option{--speller}}
-@item -s @var{program}
+@item -s "@var{program} [@var{arg} @dots{}]"
-@itemx --speller=@var{program}
+@itemx --speller="@var{program} [@var{arg} @dots{}]"
 Use the given program to do spell checking and correcting.  By default,
 @command{nano} uses the command specified in the @env{SPELL} environment
 variable.  If @env{SPELL} is not set, and @option{--speller} is
@@ -915,7 +915,7 @@ When needed, use @code{unset jumpyscrolling} instead.
 @item set softwrap
 Enable soft line wrapping for easier viewing of very long lines.
 
-@item set speller "@var{program}"
+@item set speller "@var{program} [@var{arg} @dots{}]"
 Use the given program to do spell checking and correcting.
 @xref{@option{--speller}} for details.
 

doc/nanorc.5

@@ -261,7 +261,7 @@ When needed, use \fBunset jumpyscrolling\fR instead.
 .B set softwrap
 Enable soft line wrapping for easier viewing of very long lines.
 .TP
-.B set speller "\fIprogram\fP"
+.B set speller """\fIprogram\fR [\fIarg\fR...]\fB"""
 Use the given \fIprogram\fR to do spell checking and correcting,
 instead of the built-in corrector that calls \fBspell\fR.
 .TP