add comment of potential failure due to firewall

[avallecam]

as reported in epiverse-trace/readepi#83

tutorials-early/episodes/read-cases.Rmd

Lines 164 to 173 in 9128efa

	# establish the connection to a test MySQL database
	rdbms_login <- readepi::login(
	from = "mysql-rfam-public.ebi.ac.uk",
	type = "MySQL",
	user_name = "rfamro",
	password = "",
	driver_name = "",
	db_name = "Rfam",
	port = 4497
	)