Add the CLA text to the README (#43179)

GitOrigin-RevId: 3d6b545c870d71e8d25a1e352a17b77870a8c503

Author: nipunn1313

CONTRIBUTING.md

@@ -32,3 +32,6 @@ Instructions for building and running Convex packages locally:
 Note: If you just want to self-host Convex and not modify the codebase, we
 recommend using the pre-built Docker image or binary. See the
 [self-hosted README](self-hosted/README.md) for more information.
+
+By submitting pull requests, you confirm that Convex can use, modify, copy, and
+redistribute the contribution, under the terms of its choice.

README.md

@@ -47,6 +47,8 @@ instructions. Community support for self-hosting is available in the
   discussions.
 - Report issues when building and using the open source Convex backend through
   [GitHub Issues](https://github.com/get-convex/convex-backend/issues)
+- By submitting pull requests, you confirm that Convex can use, modify, copy,
+  and redistribute the contribution, under the terms of its choice.
 
 ## Building from source