docs: say that 'cutwordright' is now bound to <Ctrl+Delete> by default

Also, suggest to rebind ^H to 'cutwordleft' so that <Ctrl+Backspace>
will delete the word to the left of the cursor (on some terminals).

doc/nano.texi

@@ -1148,9 +1148,13 @@ current cursor position.
 
 @item cutwordleft
 Cuts from the cursor position to the beginning of the preceding word.
+(This function is not bound by default.  If your terminal produces
+@code{^H} for <Ctrl+Backspace>, you can make <Ctrl+Backspace> delete
+the word to the left of the cursor by rebinding ^H to this function.)
 
 @item cutwordright
 Cuts from the cursor position to the beginning of the next word.
+(This function is bound by default to <Ctrl+Delete>.)
 
 @item cutrestoffile
 Cuts all text from the cursor position till the end of the buffer.

doc/nanorc.5

@@ -498,9 +498,13 @@ current cursor position.
 .TP
 .B cutwordleft
 Cuts from the cursor position to the beginning of the preceding word.
+(This function is not bound by default.  If your terminal produces
+\fB^H\fR for <Ctrl+Backspace>, you can make <Ctrl+Backspace> delete
+the word to the left of the cursor by rebinding ^H to this function.)
 .TP
 .B cutwordright
 Cuts from the cursor position to the beginning of the next word.
+(This function is bound by default to <Ctrl+Delete>.)
 .TP
 .B cutrestoffile
 Cuts all text from the cursor position till the end of the buffer.

doc/sample.nanorc.in

@@ -263,10 +263,14 @@
 ## Key bindings.
 ## See nanorc(5) (section REBINDING KEYS) for more details on this.
 ##
-## The following two functions are not bound to any key by default.
-## You may wish to choose other keys than the ones suggested here.
-# bind M-B cutwordleft main
-# bind M-N cutwordright main
+## The <Ctrl+Delete> keystroke deletes the word to the right of the cursor.
+## On some terminals the <Ctrl+Backspace> keystroke produces ^H, which is
+## the ASCII character for backspace, so it is bound by default to the
+## backspace function.  The <Backspace> key itself produces a different
+## keycode, which is hard-bound to the backspace function.  So, if you
+## normally use <Backspace> for backspacing and not ^H, you can make
+## <Ctrl+Backspace> delete the word to the left of the cursor with:
+# bind ^H cutwordleft main
 
 ## Set this if your Backspace key sends Del most of the time.
 # bind Del backspace all