Add high-level maintenance docs

Author: mrmundt

docs/README.md

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+# software.sandia.gov Documentation
+
+To aid future maintenance of this website, this README
+will document details that have the potential to change at
+some point in the future.
+
+## Headers and Footers
+
+The headers and footers for all pages are defined in the
+[`_includes`](https://github.com/sandialabs/sandialabs.github.io/tree/main/_includes)
+directory.
+
+- [head.html](https://github.com/sandialabs/sandialabs.github.io/blob/main/_includes/head.html) contains:
+  - Tab icon image
+  - Sandia approval information
+- [header.html](https://github.com/sandialabs/sandialabs.github.io/blob/main/_includes/header.html) contains:
+  - Navigational bar / dropdowns
+  - Social media links
+- [footer.html](https://github.com/sandialabs/sandialabs.github.io/blob/main/_includes/footer.html) contains:
+  - Sandia / NNSA logos
+  - Sandia legal/funding statement
+  - Copyright statement
+
+## Repository List
+
+The file to control what repositories are queried and cataloged can be found
+in [input_lists.json](https://github.com/sandialabs/sandialabs.github.io/blob/main/_explore/input_lists.json).
+
+- `orgs` controls GitHub organizations under which all public repositories will be queried.
+  For example, the [`mantevo` organization](https://github.com/mantevo) has 13 public repositories
+  (as of the writing of this README). All of these will be included in any query scripts
+  for software.sandia.gov.
+- `repos` controls individual repositories.
+
+## Categories
+
+The file to control categories that appear on the homepage and the catalog search
+can be found in [category_info.json](https://github.com/sandialabs/sandialabs.github.io/blob/main/category/category_info.json).
+All categories require a title (as it appears on the homepage), an icon path (with appropriate
+alternative text), a description, and the correlated GitHub "topic" (or topics).
+For example, for a repository to show up in the `BUILD TOOLS` category on
+software.sandia.gov, the repository must have the `snl-build-tools` topic
+applied on GitHub. More information on GitHub topics can be found on
+their [online documentation](https://help.github.com/articles/about-topics).
+
+## Image Source
+
+Images are stored in the [assets directory](https://github.com/sandialabs/sandialabs.github.io/tree/main/assets/images).
+Images from the original LLNL repository are also there for reference.
+
+The icons and banner image were created by Sandia's internal Creative Services
+team.
+
+## Automatic Updates
+
+Updates occur nightly via a
+[GitHub Actions workflow](https://github.com/sandialabs/sandialabs.github.io/blob/main/.github/workflows/update_data.yml).
+This job requires a `TOKEN_USER` and `SECRET_TOKEN` (both secrets on the repository)
+in order to run. Information on the `SECRET_TOKEN` requirements can be found
+in the [_explore README](https://github.com/sandialabs/sandialabs.github.io/tree/main/_explore).
+
+If the job needs to be run outside of the regular nightly cadence, a user can navigate
+to the [Actions page](https://github.com/sandialabs/sandialabs.github.io/actions/workflows/update_data.yml)
+and click the "Run workflow" button.
+
+There is a possibility in the future that the nightly query will error due to
+GitHub request limits. As of July 2024, GitHub has an hourly limit of 5000 API
+requests. If the limit is hit, processing will cease until the available
+queries reset.
+
+### Acknowledgements
+
+Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering
+Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of
+Energy’s National Nuclear Security Administration under contract DE-NA-0003525. SAND2024-09661O