Rename and alter sections of May 2013 README

Make the following changes in the README.md file for May 2013.
  1. Rename 'Time spent per day' section to 'Progress log'.
  2. Rename 'Concluding comments' section to 'Conclusion'.
  3. Display the time spent on each day in a code block.
  4. In the table of contents, add a section called
     'Introduction' that points to the beginning of the README
     file.
Add table of contents to July 2013 README