docs: add dotnet sdk

[vinckr]

Related issue

#511 (comment)

Proposed changes

Checklist

• I have read the contributing guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security. vulnerability, I
  confirm that I got green light (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further comments

[zepatrik]

Does this update everything around SDKs?

[vinckr]

Yes this adds all the sdks in https://github.com/ory/sdk/tree/master/clients/keto

[vinckr]

Or should
https://pypi.org/project/ory-keto-client/
be changed to
https://github.com/ory/sdk/tree/master/clients/keto/python
as well?

[aeneasr]

No, all SDKs should link to the released packages. I overlooked this in your other PRs. The source code doesn't really help people and could be added in parenthesis after the link to the actual package (like npm, pypi, ...)

[vinckr]

Makes sense, I will update this Pr and change the others.