Update benchmark docs yet again

ref_app/src/app/benchmark/readme.md

@@ -48,10 +48,14 @@ $\pi$ using a Gauss AGM method with help
 from the [`decwide_t`](https://github.com/ckormanyos/real-time-cpp/blob/master/ref_app/src/math/wide_decimal/decwide_t.h)
 template class.
 
-The [PDF image](https://github.com/ckormanyos/real-time-cpp/blob/update_docs/ref_app/src/app/benchmark/images/app_benchmark_pi_agm.pdf)
+The image below
 shows the real-time measurement of this benchmark
 on two of our target systems having vastly different
-performance classes:
+performance classes.
+
+![](https://github.com/ckormanyos/real-time-cpp/blob/update_docs/ref_app/src/app/benchmark/images/app_benchmark_pi_agm.pdf)
+
+Differing performance classes are compared for
 the $8$-bit MICROCHIP(R) AVR controller of the Arduino
 and the $32$-bit ARM(R) 8 controller
 of the BeagleBone Black Edition, Rev. C.