Fix bootstrap links to Boost.Build documentation

bootstrap.bat

@@ -82,7 +82,7 @@ ECHO     - Getting started guide:
 ECHO     http://boost.org/more/getting_started/windows.html
 ECHO.     
 ECHO     - Boost.Build documentation:
-ECHO     http://www.boost.org/build/doc/html/index.html
+ECHO     http://www.boost.org/build/
 ECHO.
 
 goto :end

bootstrap.sh

@@ -407,6 +407,6 @@ Further information:
      http://www.boost.org/more/getting_started/unix-variants.html
      
    - Boost.Build documentation:
-     http://www.boost.org/build/doc/html/index.html
+     http://www.boost.org/build/
 
 EOF