Add amrex topic

[WeiqunZhang]

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• I am not the sole author or employee of a company who created either the topic I am modifying/adding or the collection entry I am modifying/adding.

Which change are you proposing?

• Suggesting edits to an existing topic or collection
• Curating a new topic or collection
• Something that does not neatly fit into the binary options above

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Curating a new topic or collection

• I've formatted my changes as a new folder directory, named for the topic or collection as it appears in the URL on GitHub (e.g. https://github.com/topics/[NAME] or https://github.com/collections/[NAME])
• My folder contains a *.png image (if applicable) and index.md
• All required fields in my index.md conform to the Style Guide and API docs: https://github.com/github/explore/tree/main/docs

This helps others discover related work and strengthens the AMReX ecosystem.

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Please note: we will close your PR without comment if you do not check the boxes above and provide ALL requested information.

[jmeridth]

🛑 Thank you for the contribution ❤️. Unfortunately, as per our contribution guidelines, we don't allow self promotion if you are a direct employee of a company creating the project, or the creator and sole maintainer of the project:

Avoid conflicts of interest. These should be of general community interest, not a marketing vehicle for a product or a personal project. If you are a direct employee of a company creating the project, or the creator and sole maintainer, it’s unlikely to be accepted.

We do this so that project get curated if there is enough support/activity in the community. Thank you!

[WeiqunZhang]

@jmeridth Although I am one of the main developers of the amrex project, I am not the creator or sole maintainer of the project. The project started at LBNL, but it's now a project of the HPSF (https://hpsf.io/), which is under the Linux Foundation. Furthermore, the copyright is owned by the Linux Foundation Charities. See the bottom of https://amrex-codes.github.io/amrex/. If you need legal document regarding this, I am happy to provide it. Given these, would you reconsider this PR?

[WeiqunZhang]

To clarify, I am a employee of the Lawrence Berkeley National Laboratory, not the Linux Foundation, which now owns the project. The AMReX project was started by multiple national labs as part of the US Department of Energy's Exascale Computing Project (https://www.exascaleproject.org/).