doc(contributing): made the contributing document a bit clearer

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

CONTRIBUTING.md

@@ -2,11 +2,15 @@
 
 We want to make contributing to this project as easy and transparent as possible.
 
+Please refer to the steps described on our website: [How to contribute to OAI](https://www.openairinterface.org/?page_id=112).
+
 1. Sign and return a Contributor License Agreement to OAI team.
-2. We recommend that you provide us with a professional or student email address 
-2. Register on [Eurecom GitLab Server](https://gitlab.eurecom.fr/users/sign_in)
+2. Register on [Eurecom GitLab Server](https://gitlab.eurecom.fr/users/sign_up) if you do not have any.
+   - We recommend that you register with a professional or student email address.
+   - If your email domain (`@domain.com`) is not whitelisted, please contact us (mailto:contact@openairinterface.org).
+   - Eurecom GitLab does NOT accept public email domains.
 3. Provide the OAI team with the **username** of this account to (mailto:contact@openairinterface.org) ; we will give you the developer rights on this repository.
-4. The policies are described in these wiki pages: [OAI Policies](https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/oai-policies-home)
+4. The policies are described in these wiki pages: [OAI Policies](https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/oai-policies-home).
    - PLEASE DO NOT FORK the OAI repository on your own Eurecom GitLab account. It just eats up space on our servers.
    - You can fork onto another hosting system. But we will NOT accept a merge request from a forked repository.
       * This decision was made for the license reasons.
@@ -17,7 +21,7 @@ We want to make contributing to this project as easy and transparent as possible
 
 ## Coding Styles ##
 
-There are described [here](https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/guidelines/guidelines-home)
+There are described [here](https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/guidelines/guidelines-home).
 
 ## License ##