docs: note also in the Info manual that text can be selected with Shift

And remove a detail that is untrue when 'set selectedcolor' is used.

doc/nano.1

@@ -54,9 +54,9 @@ highlighted), and then use \fB^K\fR to cut it, or \fBM\-6\fR to copy it to the
 cutbuffer.  One can also save the marked text to a file with \fB^O\fR, or
 spell check it with \fB^T\fR.
 .PP
-Since nano-2.7.0, text can also be selected by holding Shift and moving the
-cursor with the arrow keys.  Holding down the Alt key too will increase the
-stride.
+On some terminals, text can be selected also by holding down Shift while
+using the arrow keys.  Holding down the Alt key too will increase the stride.
+Any cursor movement without Shift being held will cancel such a selection.
 .PP
 The two lines at the bottom of the screen show some important commands;
 the built-in help (\fB^G\fR) lists all the available ones.

doc/nano.texi

@@ -497,12 +497,15 @@ the 'Copy Text' command (default key binding: @kbd{M-6}).
 
 Text can be selected by first 'setting the Mark' (default key bindings:
 @kbd{^6} and @kbd{M-A}) and then moving the cursor to the other end of the portion
-to be selected.  The selected portion of text will be highlighted in
-reverse video (or in bold if you set the boldtext option).
+to be selected.  The selected portion of text will be highlighted.
 This selection can now be cut or copied in its entirety with a single
 @kbd{^K} or @kbd{M-6}.  Or the selection can be used to limit the scope of
 a search-and-replace (@kbd{^\}) or spell-checking session (@kbd{^T}).
 
+On some terminals, it is also possible to select text by holding down
+@kbd{Shift} together with the cursor keys.  Such a selection is cancelled
+upon any cursor movement where @kbd{Shift} isn't held.
+
 Cutting or copying selected text will toggle the mark off automatically.
 If necessary, it can be toggled off manually with another @kbd{^6} or @kbd{M-A}.