[PR #3804] a couple of wording tweaks from PR review [ci skip]

Signed-off-by: Mats Wichmann <[email protected]>

Author: mwichmann

SCons/Environment.xml

@@ -3250,7 +3250,7 @@ command-line option.
 </para>
 
 <para>
-Physically duplicating the source files may be disabled by setting the
+Duplicating the source files may be disabled by setting the
 <parameter>duplicate</parameter>
 argument to
 <constant>False</constant>.

doc/user/separate.xml

@@ -166,7 +166,7 @@ int main() { printf("Hello, world!\n"); }
 
     <para>
 
-    The main thing to understand is that when you set up a variant directory,
+    The important thing to understand is that when you set up a variant directory,
     &SCons; performs the build <emphasis>in that directory</emphasis>.
     It turns out it's easiest to ensure where build products end up
     by just building in place.