docs(aio): Add resources contributor info

aio/content/marketing/resources-contributing.md

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+# Contributing to resources.json
+
+## About this list
+We maintain a small list of some of the top Angular resources from across the community, stored in `resources.json`. This list is not intended to be comprehensive, but to act as a starting point to connect Angular developers to the rest of the community.
+
+## How do I get listed?
+While we can't accept all contributions, qualifying contributions can be submitted via a PR adding yourself to the `resources.json` file. All contributions should be in the appropriate section and must meet the following criteria:
+
+1. Your contribution must be valid, and contain a link to a page talking specifically about using Angular
+1. Your contribution should have a clear and concise title and description
+1. Your resource should follow our brand guidelines (see our [Presskit](https://angular.io/presskit))
+1. Your resource should have significant benefit to Angular developers
+1. Your resource should already have traction and praise from Angular developers