Modify documentation re file-based configuration to respond to proble…

…m raised by gerdr++ in #233.

Configure.pl

@@ -458,6 +458,13 @@ =head1 CONFIGURATION-FILE INTERFACE
 ... you would now place the assignments to C<CC> and C<CX> in the
 I<=variables> section of the configuration file (as above).
 
+In addition, should you wish to use an option whose value contains whitespace
+and would, if presented on the command-line, require quoting, you should
+assign that string to a variable and then use the variable in the C<general>
+section below.
+
+    LONGLONG=long long
+
 =back
 
 =item * general
@@ -485,6 +492,8 @@ =head1 CONFIGURATION-FILE INTERFACE
 Note that when the value is a variable defined in the I<=variables> section,
 it must be preceded by a C<$> sign.
 
+    intval=$LONGLONG
+
 =item *
 
 You I<may> list options here which are I<conceptually> limited to a single