docs: add two examples of the 'tabgives' command to the sample nanorc

doc/sample.nanorc.in

@@ -261,6 +261,14 @@
 # include "@PKGDATADIR@/*.nanorc"
 
 
+## If <Tab> should always produce four spaces when editing a Python file,
+## independent of the settings of 'tabsize' and 'tabstospaces':
+# extendsyntax python tabgives "    "
+#
+## If <Tab> should always produce an actual TAB when editing a Makefile:
+# extendsyntax makefile tabgives "	"
+
+
 ## Key bindings.
 ## See nanorc(5) (section REBINDING KEYS) for more details on this.