[Docs] Minor fixes: Typos, Formatting, Links, Sample code
minor #246 [Docs] Minor fixes: Typos, Formatting, Links, Sample code (bicpi)

This PR was merged into the 2.2 branch.

Discussion
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[Docs] Minor fixes: Typos, Formatting, Links, Sample code

* The API link for ``ParamConverterInterface`` did not work so I've removed it
* In the overall annotation code example I've changed the template name ``post.html.twig`` to ``show.html.twig`` so the following statement in the doc becomes true: *As the `showAction` method follows some conventions, you can omit some annotations:*

Commits
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2fb2a69 [Docs] Minor fixes: Typos, Formatting, Links, Sample code