Update README and docs for running Storybook locally in DCR

Update 09 Jan

@tjmw reported that hot module reloading is broken in storybook. They also reported that browser refreshing also didn't force changes to appear, this could only be achieved by killing the storybook process and restarting the server.

This happened when running pnpm storybook:dcr from the root of the repo and when running make storybook-dev from the dotcom-rendering sub-folder.

Also, the README has now slipped further out of date as the repo now uses pnpm rather than yarn.

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A developer from another team was following the instructions on the README to get storybook running for DCR locally.

The README says: https://github.com/guardian/dotcom-rendering/blob/eed2fc61a626fd8e287d845a1a64a02d7302b088/README.md?plain=1#L23-L25

Though I think the advice is now to install from each sub directory (apps-rendering,dotcom-rendering)?

It also says: https://github.com/guardian/dotcom-rendering/blob/eed2fc61a626fd8e287d845a1a64a02d7302b088/README.md?plain=1#L27-L29

Though this isn't obvious as we have commands to run storybook at the root package.json https://github.com/guardian/dotcom-rendering/blob/eed2fc61a626fd8e287d845a1a64a02d7302b088/package.json#L22-L27

These commands no longer work properly. yarn storybook errors and yarn storybook:dcr hangs launches but quietly, leaving the developer to think that it hangs...

[!IMPORTANT] Should we remove these root yarn commands?

We should also update the README with up-to-date instructions on how to get started with this repo.