sdbus++: async: client: example: add a few comments for clarity

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Idf21e9652c005203a3f563b46605354e4711183d
diff --git a/example/calculator-client.cpp b/example/calculator-client.cpp
index 0fe8420..6bb2bc7 100644
--- a/example/calculator-client.cpp
+++ b/example/calculator-client.cpp
@@ -16,26 +16,32 @@
     // been used to combine multiple interfaces into a single client-proxy.
 
     {
+        // Call the Multiply method.
         auto _ = co_await c.multiply(7, 6);
         std::cout << "Should be 42: " << _ << std::endl;
     }
 
     {
+        // Get the LastResult property.
         auto _ = co_await c.lastResult();
         std::cout << "Should be 42: " << _ << std::endl;
     }
 
     {
+        // Call the Clear method.
         co_await c.clear();
     }
 
     {
+        // Get the LastResult property.
         auto _ = co_await c.lastResult();
         std::cout << "Should be 0: " << _ << std::endl;
     }
 
     {
+        // Set the LastResult property.
         co_await c.lastResult(1234);
+        // Get the LastResult property.
         auto _ = co_await c.lastResult();
         std::cout << "Should be 1234: " << _ << std::endl;
     }