Add EasyCLA info (#290)

Signed-off-by: Brian Warner <[email protected]>

README.md

@@ -191,6 +191,16 @@ in a terminal. This will watch the file system run lint, tests, and type checkin
 
 To lint the JS files and run type interface checks run `npm run lint`.
 
+### Opening a PR
+
+This repository is managed by EasyCLA. Project participants must sign the free ([GraphQL Specification Membership agreement](https://preview-spec-membership.graphql.org) before making a contribution. You only need to do this one time, and it can be signed by [individual contributors](http://individual-spec-membership.graphql.org/) or their [employers](http://corporate-spec-membership.graphql.org/).
+
+To initiate the signature process please open a PR against this repo. The EasyCLA bot will block the merge if we still need a membership agreement from you.
+
+You can find [detailed information here](https://github.com/graphql/graphql-wg/tree/main/membership). If you have issues, please email [[email protected]](mailto:[email protected]).
+
+If your company benefits from GraphQL and you would like to provide essential financial support for the systems and people that power our community, please also consider membership in the [GraphQL Foundation](https://foundation.graphql.org/join).
+
 ## License
 
 graphql-relay-js is [MIT licensed](./LICENSE).