doc: update 'Troubleshooting' section

It doesn't matter anymore if there are many off nodes, because the registry
only queries the addresses of nodes that are in the routing table.

docs/re6stnet.rst

@@ -142,10 +142,10 @@ be able to connect to it.
 TROUBLESHOOTING
 ===============
 
-On networks with very few working nodes compared to the total number of
-registered nodes, it may take some time to bootstrap. However, if you really
-think something goes wrong, you should first enable OpenVPN logs and increase
-verbosity: see commented directives in configuration generated by `re6st-conf`.
+When many nodes are saturated or behind unconfigurated NAT, it may take
+some time to bootstrap. However, if you really think something goes wrong,
+you should first enable OpenVPN logs and increase verbosity:
+see commented directives in configuration generated by `re6st-conf`.
 
 A common failure is caused by a misconfigured firewall: