docs: specify finding unassigned good first issues (#75)

Author: JoshuaKGoldberg

.github/CONTRIBUTING.md

@@ -24,7 +24,7 @@ There are two steps involved:
 ### Finding an Issue
 
 With the exception of very small typos, all changes to this repository generally need to correspond to an [open issue marked as `accepting prs` on the issue tracker](https://github.com/JoshuaKGoldberg/template-typescript-node-package/issues?q=is%3Aopen+is%3Aissue+label%3A%22accepting+prs%22).
-If this is your first time contributing, consider searching for [issues that also have the `good first issue` label](https://github.com/JoshuaKGoldberg/template-typescript-node-package/issues?q=is%3Aopen+is%3Aissue+label%3A%22accepting+prs%22+label%3A%22good+first+issue%22).
+If this is your first time contributing, consider searching for [unassigned issues that also have the `good first issue` label](https://github.com/JoshuaKGoldberg/template-typescript-node-package/issues?q=is%3Aopen+is%3Aissue+label%3A%22accepting+prs%22+label%3A%22good+first+issue%22+no%3Aassignee).
 If the issue you'd like to fix isn't found on the issue, see [Reporting Issues](#reporting-issues) for filing your own (please do!).
 
 ### Sending a Pull Request