Updated privacy policy.

privacy_policy.md

@@ -9,6 +9,8 @@
   - [Cookie policy](#cookie-policy)
     - [Legal](#legal)
   - [Accounts](#accounts)
+    - [GitHub OAuth2 authentication](#github-oauth2-authentication)
+    - [Traditional accounts](#traditional-accounts)
 
 <!--TOC-->
 
@@ -73,5 +75,33 @@ This website uses:
 
 ## Accounts
 
-Registration is disabled to avoid spammers,
-however if you want an account you can contact me.
+To create a new account the only information needed are:
+
+- a username
+- an email
+- a password which not readable by the administrator in plaintext form
+
+For the moment, repository creation is disabled.
+
+An account gives you the possibility to interact with the issue trackers on
+this instance.
+
+### GitHub OAuth2 authentication
+
+You can create an account using GitHub
+at https://software.franco.net.eu.org/user/oauth2/software.franco
+
+If you select this type of authentication GitHub
+[terms](https://docs.github.com/en/github/site-policy/github-terms-of-service)
+and
+[privacy policy](https://docs.github.com/en/github/site-policy/github-privacy-statement)
+apply.
+
+Please note that you cannot change the username once the account is created because
+this type of authentication is external. To change username you must first delete
+your account and then create a new one.
+
+### Traditional accounts
+
+Traditional registration is disabled to avoid spammers,
+however if you want an account of this type you can contact me.