docs: mention the default values for comment and whitespace directives

Also, use proper mark-up for the examples.

doc/nano.texi

@@ -932,13 +932,14 @@ system and will be silently ignored otherwise.
 
 @item comment "string"
 Use the given string for commenting and uncommenting lines.  A vertical bar or
-pipe character (|) designates bracket-style comments; for example, "/*|*/" for
+pipe character (@t{|}) designates bracket-style comments; for example, @t{"/*|*/"} for
 CSS files.  The characters before the pipe are prepended to the line and the
 characters after the pipe are appended at the end of the line.  If no pipe
-character is present, the entire string is prepended; for example, "#" for
+character is present, the entire string is prepended; for example, @t{"#"} for
 Python files.  If empty double quotes are specified, the comment/uncomment
-functions are disabled; for example, "" for JSON.  Double quotes or backslashes
-may be escaped with a backslash; for example, ".\\"" for man page source.
+functions are disabled; for example, @t{""} for JSON.  Double quotes or backslashes
+may be escaped with a backslash; for example, @t{".\\""} for man page source.
+The default value is @t{"#"}.
 
 @item color fgcolor,bgcolor "regex" @dots{}
 Display all pieces of text that match the

doc/nanorc.5

@@ -270,7 +270,8 @@ Disallow file modification.
 .TP
 .B set whitespace "\fIstring\fP"
 Set the two characters used to indicate the presence of tabs and
-spaces.  They must be single-column characters.
+spaces.  They must be single-column characters.  The default pair
+for a UTF-8 locale is "\fB»·\fR", and for other locales "\fB>.\fR".
 .TP
 .B set wordbounds
 Detect word boundaries differently by treating punctuation
@@ -329,13 +330,14 @@ system and will be silently ignored otherwise.
 .TP
 .BI comment " string"
 Use the given string for commenting and uncommenting lines.  A vertical bar or
-pipe character (|) designates bracket-style comments; for example, "/*|*/" for
+pipe character (\fB|\fP) designates bracket-style comments; for example, "\fB/*|*/\fP" for
 CSS files.  The characters before the pipe are prepended to the line and the
 characters after the pipe are appended at the end of the line.  If no pipe
-character is present, the entire string is prepended; for example, "#" for
+character is present, the entire string is prepended; for example, "\fB#\fP" for
 Python files.  If empty double quotes are specified, the comment/uncomment
 function is disabled; for example, "" for JSON.  Double quotes or backslashes
-may be escaped with a backslash; for example, ".\\"" for man page source.
+may be escaped with a backslash; for example, "\fB.\\"\fP" for man page source.
+The default value is "\fB#\fP".
 .TP
 .B color \fIfgcolor\fR,\fIbgcolor\fR """\fIregex\fR""" ...
 Display all pieces of text that match