explain that some usernames are sensitive

tsa/doc/accounts.creole

@@ -89,6 +89,30 @@ in the {{{Tor Sysadmin Team}}} component:
   file for them.  Please enclose the OpenPGP clearsigned blob using
   {{{{{{}}} and {{{}}}}}}.
 
+The username should be checked for conflict with commonly used
+adminstrative aliases (`root`, `abuse`, ...) or abusive names
+(`killall*`, ...). In particular, the following have special meaning
+for various services and should be avoided:
+
+    root
+    abuse
+    arin-admin
+    certmaster
+    domainadmin
+    hostmaster
+    mailer-daemon
+    postmaster
+    security
+    webmaster
+
+That list, [[taken from the leap
+project|https://leap.se/git/leap_platform.git/blob/HEAD:/puppet/modules/site_postfix/manifests/mx/static_aliases.pp]]
+is not exhaustive and your own judgement should be used to spot
+possibly problematic aliases. See also those other possible lists:
+
+ * [[systemli|https://github.com/systemli/userli/blob/master/config/reserved_names.txt]]
+ * [[LEAP|https://leap.se/git/leap_platform.git/blob/HEAD:/puppet/modules/site_postfix/manifests/mx/static_aliases.pp]]
+
 === Step n+1 ===
 
 Once the request has been filed it will be reviewed by Roger or Nick