docs: add notes to draw attention to the changed defaults

doc/nano.1

@@ -25,6 +25,16 @@ nano \- Nano's ANOther editor, inspired by Pico
 .B nano
 .RI [ options "] [[+" line [, column "]]\ " file "]..."
 
+.SH NOTE
+Starting with version 4.0, \fBnano\fR no longer hard-wraps an overlong
+line by default, and no longer automatically adds a newline at the end
+of the text if one is missing.  Furthermore, it uses smooth scrolling
+by default and makes use of the line below the title bar.
+.sp
+If you want the old, Pico behavior back, please use \fB\-\-breaklonglines\fR,
+\fB\-\-finalnewline\fR, \fB\-\-jumpyscrolling\fR, and \fB\-\-emptyline\fR
+(or \fB\-bfje\fR for short).
+
 .SH DESCRIPTION
 \fBnano\fP is a small and friendly editor.  It copies the look and feel
 of Pico, but is free software, and implements several features that Pico

doc/nano.texi

@@ -96,6 +96,15 @@ as is reasonable while offering a superset of Pico's functionality.
 @xref{Pico Compatibility} for more details on how @command{nano} and
 Pico differ.
 
+Starting with version 4.0, @command{nano} no longer hard-wraps an overlong
+line by default, and no longer automatically adds a newline at the end
+of the text if one is missing.  Furthermore, it uses smooth scrolling
+by default and makes use of the line below the title bar.
+
+If you want the old, Pico behavior back, please use @option{--breaklonglines},
+@option{--finalnewline}, @option{--jumpyscrolling}, and @option{--emptyline}
+(or @option{-bfje} for short).
+
 Please report bugs via @url{https://savannah.gnu.org/bugs/?group=nano}.
 
 

doc/nanorc.5

@@ -21,6 +21,15 @@
 .SH NAME
 nanorc \- GNU nano's configuration file
 
+.SH NOTE
+Starting with version 4.0, \fBnano\fR no longer hard-wraps an overlong
+line by default, and no longer automatically adds a newline at the end
+of the text if one is missing.  Furthermore, it uses smooth scrolling
+by default and makes use of the line below the title bar.
+.sp
+If you want the old, Pico behavior back, please use \fBset breaklonglines\fR,
+\fBset finalnewline\fR, \fBset jumpyscrolling\fR, and \fBset emptyline\fR.
+
 .SH DESCRIPTION
 The \fInanorc\fP file contains the default settings for \fBnano\fP, a
 small and friendly editor.  The file should be in Unix format, not in