README: Add an example for using option -D

Change-Id: I1a4e43944e89ee160ca703a4976db90554f35402
Signed-off-by: Vishwanatha Subbanna <vishwa@linux.vnet.ibm.com>
diff --git a/README.md b/README.md
index 7b38083..41d0d66 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@
 - com/ibm - `-Ddata_com_ibm=true`
 - org/open_power - `-Ddata_org_open_power=true`
 
+Example: `meson builddir -Ddata_com_ibm=true && ninja -C builddir`
 ## References
 
 [sdbusplus binding generation tool sdbus++]: https://github.com/openbmc/sdbusplus/blob/master/README.md#binding-generation-tool