add short Readme

Demos/Readme_demos.rst

+* To run demos do::
+
+    cd Demos
+    make test
+
+  which runs run_primes.py, run_numeric_demo.py, run_spam.py,
+  integrate_timing.py, callback/runcheese.py and embed/embedded
+
+* For other demos::
+
+    cd libraries
+    python setup.py build_ext --inplace
+    python -c 'import call_mymath;print(call_mymath.call_sinc(1))'
+
+  To run one of the benchmarks for 10 iterations to compare cython and python::
+
+    cd benchmarks
+    python nqueens.py -n 10
+    python -c 'import nqueens;print(nqueens.test_n_queens(10))'
+    
+* Known failures
+
+  * benchmarks/chaos.py failing for both python2 and python3
+
+  * embed and freeze work for python2, compile but fail for python3
+

Demos/benchmarks/Readme_benchmarks.rst

-To run a benchmark:
-
-10 iterations, python::
-
-  python nqueens.py -n 10
-
-
-10 iterations, cython::
-
-  python -c 'import nqueens;print(nqueens.test_n_queens(10))'
-