Add reference to the reason behind the native/emulated FPU compilation of the...

Add reference to the reason behind the native/emulated FPU compilation of the BSP (from the RTEMS list)

OAR/README.md

@@ -9,6 +9,17 @@ source code demonstrates how to:
 * support targetting Leon2 and Leon3 CPUs
 * enable/disable showing compilation commands
 
+Building RTEMS via the RSB
+--------------------------
+The contrib folder includes a script that you can use to compile RTEMS4.11
+with the Leon2 and Leon3 BSPs from the OAR repository. Note that
+[as discussed in the RTEMS mailing list](https://lists.rtems.org/pipermail/users/2016-February/029782.html),
+you will need to compile your BSP for native or emulated FPU, based
+on what your desired target is (i.e. edit the leon2.cfg/leon3.cfg 
+files to remove `-msoft-float` or not). The Makefile mirrors this
+need, by pointing to different paths (see FPU_SUFFIX variable),
+depending on whether you build with FPU=1 or not.
+
 Application sources
 -------------------
 The sources of your project must be set inside the Makefile, in the SRC