Add missing dependency for HttpFragmentServiceProvider

WebProfilerBundle templates make use of `render` functions. This means it requires the `HttpFragmentServiceProvider` to be enabled. This updates the readme accordingly.
minor #51 Add missing dependency for HttpFragmentServiceProvider (henrikbjorn)

This PR was merged into the 2.0.x-dev branch.

Discussion
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Add missing dependency for HttpFragmentServiceProvider

WebProfilerBundle templates make use of `render` functions. This means it requires the `HttpFragmentServiceProvider` to be enabled. This updates the readme accordingly.

Commits
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ad5719b Add missing dependency for HttpFragmentServiceProvider