Add README.md for script

scripts/gh_scripts/README.md

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+# GitHub Project Management Scripts
+
+This directory contains scripts that the Open Library team uses to interact with this GitHub repository.
+
+## `auto_unassigner.mjs`
+
+This script fetches all open issues that have assignees and automatically removes assignees that meet the following criteria:
+- Assignee has been assigned for more than 14 days and has not created and linked a pull request to the issue.
+- Assignee's GitHub username does not appear on the exclude list.
+
+This script skips over issues that have the `no-automation` label.
+
+This script takes two options:
+- `--daysSince` Integer that defines the number of days until an assignee is stale.  Defaults to `14`.
+- `--repoOwner` String that defines the specific `openlibrary` repository.  Defaults to `internetarchive`.
+
+> [!IMPORTANT]
+> Include a space between an option and its value when calling this script.
+
+__Correct:__
+`node auto_unassigner.mjs --daysSince 21`
+
+__Incorrect:__
+`node auto_unassigner.mjs --daysSince=21`
+
+The GitHub action that runs this script automatically sets `--repoOwner` to the owner of the repository that triggered the action.