[doc] added an example about how to call vpr

docs/source/manual/openfpga_shell/openfpga_commands/vpr_commands.rst

@@ -10,6 +10,19 @@ vpr
 
   .. note:: This command will run vpr in a standalone way, whose results will be kept and used by other commands. Suggest to use when this is the final run of VPR.
 
+  For example, vpr commands may be called in the following way:
+
+.. code-block:: shell
+
+  # VPR standalone runs, no results will be kept for downstream commands
+  vpr_standalone <some_options> 
+  vpr_standalone <some_options> 
+  # More standalone runs may be expected
+  vpr_standalone <some_options> 
+  # Final VPR run, results are kept for downstream commands
+  vpr <some_options>
+  # Other commands that use VPR results
+
 .. _vtr_project: https://github.com/verilog-to-routing/vtr-verilog-to-routing
 
 vpr_standalone