feat: Update Readme with PhysilbAlpha

[jstoobysmith]

Updating the Readme with a description of PhysilbAlpha.

[github-actions]

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[morrison-daniel]

We may want to describe what the review standard is, even if it is low so it's clear why a PR would pass/not pass

[jstoobysmith]

@morrison-daniel Done

[morrison-daniel]

I'll approve so you can merge if you want, but feel free to wait for more feedback

[morrison-daniel]

Suggested change

PhyslibAlpha sits downstream of `./Physlib` (within the same repository). The core idea is that PhyslibAlpha has a lower review-standards then Physlib making it easier to get large PRs, AI-generated content, or formalizations which are not-quite-perfect in. PRs for PhyslibAlpha must pass basic linter checks, described [here](https://github.com/leanprover-community/physlib/blob/master/scripts/PhyslibAlpha/README.md). PRs must also undergo a light 'one-look' review checking 1) Whether the content is main-stream physics, 2) Whether it looks reasonable (no axioms, easy to read etc.), 3) Whether it is within the right place within PhyslibAlpha (mirroring its place in Physlib).

PhyslibAlpha sits downstream of `./Physlib` (within the same repository). The core idea is that PhyslibAlpha has a lower review-standards then Physlib making it easier to contribute large PRs, AI-generated content, or formalizations which are not-quite-perfect. PRs for PhyslibAlpha must pass basic linter checks, described [here](https://github.com/leanprover-community/physlib/blob/master/scripts/PhyslibAlpha/README.md). PRs must also undergo a light 'one-look' review checking 1) Whether the content is main-stream physics, 2) Whether it looks reasonable (no axioms, easy to read etc.), 3) Whether it is within the right place within PhyslibAlpha (mirroring its place in Physlib).

Small fix to make the sentence easier to read