Grammar, typos, wording fixes

[ThomasWaldmann]

Just taking notes for misc grammar / typo fixes:

• You didn't have any keys yet. --> You don't have any keys.
• This app is a slim-down version --> ... slimmed-down ...
• Currently, it support Django --> ... supports ...
• Server rp id for FIDO2, it the full domain of your project --> ... use the full domain (but without hostname like "www.") of your project
• but it needs blocks named head & content to added its content to it. --> ... to add its content to them.
• <a href="{% url 'passkeys:home' %}">Passkeys</a> --> ...Manage Passkeys...
• login form e.g 'loginForm' --> ... e.g. ...
• Finally, In your login.html --> ..., in ...
• <button class="btn btn-block btn-dark" ... --> add </button>
• For Example, See 'example' app and look at EXAMPLE.md to see how to set it up. --> For more information about how to set it up, please see the 'example' app and the EXAMPLE.md document.
• paramters --> parameters

In case I get this stuff working, I might make a PR...