Merge pull request #2891 from nouiz/doc_prof_opt

[WIP] Start of the doc how to profile Theano opt

Merge pull request #2891 from nouiz/doc_prof_opt
c5711d7a · Pascal Lamblin · 490dd097 · ce672f92 · c5711d7a
--- a/doc/extending/optimization.txt
+++ b/doc/extending/optimization.txt