Adding more clear installation instructions

[Sanidhyafeaturist]

No description provided.

[TTimo]

LGTM - @smcv do these updates look ok to you?

We mostly use toolbox these days though, that may be better to document than the podman instructions.

[smcv]

The text being added here is not really documenting the same thing as the text being deleted here: the deleted text is describing how to install/obtain the runtime, but the added text is describing the SDK. I think we should be careful not to discard existing information unless we're sure that it's useless.

We already have documentation elsewhere for how to obtain and how to run the various SDKs: see https://gitlab.steamos.cloud/steamrt/scout/sdk, https://gitlab.steamos.cloud/steamrt/soldier/sdk, https://gitlab.steamos.cloud/steamrt/sniper/sdk (which I think are referenced from elsewhere in this repo, but possibly not from the README).

Podman and Toolbx do use the same storage for containers and images, so an image that you have fetched with podman pull can be used with Toolbx and vice versa.

[Sanidhyafeaturist]

I can see, I will try to add further installation instructions

[Sanidhyafeaturist]

You should see the pull request #696