Update broken USAGE link

Signed-off-by: Steven Esser <[email protected]>

Author: steven-esser

README.rst

@@ -64,9 +64,10 @@ or on windows::
     configure
 
 
-USAGE
+REFERENCE
 -----
-See https://github.com/nexB/aboutcode-toolkit/blob/master/USAGE.rst for USAGE.
+See https://github.com/nexB/aboutcode-toolkit/blob/master/REFERENCE.rst for reference
+on aboutcode-toolkit usage.
 
 
 TESTS and DEVELOPMENT
@@ -121,4 +122,4 @@ See (of course) the about.ABOUT file for details.
     :alt: Windows Master branch tests status
 .. |devel-win| image:: https://ci.appveyor.com/api/projects/status/uwj2gh8i9ga1mqwn/branch/develop?png=true
     :target: https://ci.appveyor.com/project/nexB/aboutcode-toolkit
-    :alt: Windows Develop branch tests status
+    :alt: Windows Develop branch tests status