[doc][user][faq] Enforce institutional email in documentation

Fixes #544

doc/user/faq.rst

@@ -264,7 +264,8 @@ What is a supervisor?
 
 A supervisor is a recognized person on the platform. The supervisor is
 generally a person that holds a senior position in a laboratory/research
-institute or company.
+institute or company. It is important to note that your email should be
+institutional!
 
 
 Why do I need a supervisor to start using the |project| platform?
@@ -273,12 +274,14 @@ Why do I need a supervisor to start using the |project| platform?
 Supervisors ensure you belong to a work group.  They are institutionally
 responsible that you follow the |project| platform terms of use.  To
 successfully register, you'll need to specify the username of a *currently
-existing* supervisor on the platform.  After you have validated your e-mail
-address, a request will be made to such an user in order to confirm your
+existing* supervisor on the platform.  After you have validated your institutional
+e-mail address, a request will be made to such an user in order to confirm your
 registration.  Once the supervisor has confirmed your affiliation, your account
 becomes active and you can use the platform.  Re-activation is required after a
 period of time (usually every year).
 
+It is important to note that your email should be institutional!
+
 If your supervisor is not registered on the |project| platform, ask them to
 register, and to make a request to become a supervisor (see text below).  Once
 their account is created, you will then be able to make a supervision request
@@ -315,7 +318,7 @@ To become a supervisor, there are two ways.
 
 * Sign up on the platform and `register as a supervisor`_.
 
-    After you have validated that your email is correct, a request will then be
+    After you have validated that your institutional email is correct, a request will then be
     made to the |project| admins in order to validate your account. After
     checking, that you hold a position in your university/research institute or
     laboratory, an admin of the platform will accept your request.