Document email-consistency requirement for membership verification

README.md

@@ -21,6 +21,8 @@ Because we are legally under a nonprofit—[Metagov](https://metagov.org/) is ou
 - **Access:** private AI inference through the cooperative's gateway
 - **Governance:** members participate in decisions about models, priorities, and direction
 
+**Important:** your email address on Open Collective and on Cloudron must match. Membership is verified by matching the email you use to contribute on Open Collective against the email you use to log in. If they differ, you won't be recognized as a member. (Guest contributors — those who contribute without an Open Collective account — are recognized by the email they entered at checkout.)
+
 ## The stack
 
 The Inference Cooperative runs a self-hosted stack on [Cloudron](https://cloudron.io), with all inference routed through a single gateway to cloud-based LLM providers.