Update intro.rst - Included links to Symfony2, Pimple and Sinatra

Included links to Symfony2, Pimple and Sinatra
merged branch royopa/patch-1 (PR #789)

This PR was submitted for the master branch but it was merged into the 1.0 branch instead (closes #789).

Discussion
----------

Update intro.rst - Included links to Symfony2, Pimple and Sinatra

Included links to Symfony2, Pimple and Sinatra

Commits
-------

f9c13a1 Update intro.rst - Included links to Symfony2, Pimple and Sinatra