docs: remove the mention of backslashes for the argument of 'comment'

Also remove the backslashes from the two syntaxes that contained them.

This completes the fix for https://savannah.gnu.org/bugs/?51370.

doc/nano.texi

@@ -933,14 +933,14 @@ file.  This functionality only works when libmagic is installed on the
 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 (@t{|}) designates bracket-style comments; for example, @t{"/*|*/"} for
+Use the given string for commenting and uncommenting lines.
+If the string contains a vertical bar or pipe character (@t{|}),
+this 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, @t{"#"} for
+character is present, the full string is prepended; for example, @t{"#"} for
 Python files.  If empty double quotes are specified, the comment/uncomment
-functions are disabled; for example, @t{""} for JSON.  Backslashes and double quotes
-should be escaped with a backslash; for example, @t{".\\\""} for man page source.
+functions are disabled; for example, @t{""} for JSON.
 The default value is @t{"#"}.
 
 @item color fgcolor,bgcolor "regex" @dots{}

doc/nanorc.5

@@ -329,14 +329,14 @@ functionality only works when \fBlibmagic\fP is installed on the
 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 (\fB|\fP) designates bracket-style comments; for example, "\fB/*|*/\fP" for
+Use the given string for commenting and uncommenting lines.
+If the string contains a vertical bar or pipe character (\fB|\fR),
+this designates bracket-style comments; for example, "\fB/*|*/\fR" 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, "\fB#\fP" for
-Python files.  If empty double quotes are specified, the comment/uncomment
-function is disabled; for example, "" for JSON.  Backslashes and double quotes
-should be escaped with a backslash; for example, "\fB.\\\"\fP" for man page source.
+character is present, the full string is prepended; for example, "\fB#\fR"
+for Python files.  If empty double quotes are specified, the comment/uncomment
+function is disabled; for example, "" for JSON.
 The default value is "\fB#\fP".
 .TP
 .B color \fIfgcolor\fR,\fIbgcolor\fR """\fIregex\fR""" ...

syntax/groff.nanorc

 ## Here is an example for groff.
 
 syntax "groff" "\.m[ems]$" "\.rof" "\.tmac$" "^tmac."
-comment ".\\\""
+comment ".\""
 
 # The argument of .ds or .nr
 color cyan "^\.(ds|nr) [^[:space:]]*"

syntax/man.nanorc

@@ -2,7 +2,7 @@
 
 syntax "man" "\.[1-9]x?$"
 magic "troff or preprocessor input text"
-comment ".\\\""
+comment ".\""
 
 color green "\.(SH|SS|TH) .*$"
 color brightgreen "\.(SH|SS|TH) " "\.([HIT]P)"