docs: describe nano more specifically as a text editor

Especially the first sentences introducing nano should use the words
"text editor" and not just "editor".

doc/nano.1

@@ -19,7 +19,7 @@
 .TH NANO 1 "version 7.2" "January 2023"
 
 .SH NAME
-nano \- Nano's ANOther editor, inspired by Pico
+nano \- Nano's ANOther text editor, inspired by Pico
 
 .SH SYNOPSIS
 .B nano
@@ -31,7 +31,7 @@ nano \- Nano's ANOther editor, inspired by Pico
 .BR nano " [" \fIoptions "] [[" + [ crCR ]{ / | ? } \fIstring "] " \fIfile ]...
 
 .SH DESCRIPTION
-\fBnano\fP is a small and friendly editor.  It copies the look and feel
+\fBnano\fP is a small and friendly text editor.  It copies the look and feel
 of Pico, but is free software, and implements several features that Pico
 lacks, such as: opening multiple files, scrolling per line, undo/redo,
 syntax coloring, line numbering, and soft-wrapping overlong lines.

doc/nano.texi

@@ -35,7 +35,7 @@ The complete manual for the GNU nano text editor.
 
 @page
 
-This manual documents the GNU @command{nano} editor.
+This manual documents the GNU @command{nano} text editor.
 @sp 1
 The contents of this manual are part of the GNU @command{nano} distribution.
 

doc/nanorc.5

@@ -23,7 +23,7 @@ nanorc \- GNU nano's configuration file
 
 .SH DESCRIPTION
 The \fInanorc\fP files contain the default settings for \fBnano\fP,
-a small and friendly editor.  During startup, if \fB\-\-rcfile\fR
+a small and friendly text editor.  During startup, if \fB\-\-rcfile\fR
 is not given, \fBnano\fR will read two files: first the
 system-wide settings, from \fI/etc/nanorc\fP (the exact path might be
 different on your system), and then the user-specific settings, either