Add documentation on the new support

Author: Jlalond

lldb/bindings/interface/SBProgressDocstrings.i

@@ -52,6 +52,13 @@ Non-deterministic progresses behave the same, but omit the total in the construc
     # Explicitly send a progressEnd, otherwise this will be sent
     # when the python runtime cleans up this object.
     non_deterministic_progress.Finalize()
+
+Additionally for Python, progress is supported in a with statement. ::
+    with lldb.SBProgress('Non deterministic progress, 'Detail', lldb.SBDebugger) as progress:
+        for i in range(10):
+            progress.Increment(1)
+    # The progress object is automatically finalized when the with statement
+
 ") lldb::SBProgress;    
 
 %feature("docstring",