added doc to what the file do and why it is usefull.

theano/misc/check_blas.py

+#print info to check we link with witch version of blas
+#test the speed of the blas gemm fct:
+#C=a*C+dot(A,B)*b
+#A,B,C matrix
+#a,b scalar
+
 import theano,numpy,time
 import theano.tensor as T