Add note to README.md: queue.identify() returns string instead of uuid type

[oleg-jukovec]

See:

queue/queue/abstract/queue_session.lua

Line 195 in 813be24

cur_uuid = uuid.bin()

https://www.tarantool.io/ru/doc/latest/reference/reference_lua/uuid/#lua-function.uuid.bin

AFAIU it was done for a reason:
#139 (comment)

But it was unexpected for me as a user. I think we need to add a note into the queue.identify() description:

queue/README.md

Lines 466 to 495 in 813be24

	## Session identify
	```lua
	queue.identify(session_uuid)
	```
	In the queue the session has a unique UUID and many connections may share one
	logical session. Also, the consumer can reconnect to the existing session during
	the`ttr` time.
	To get the UUID of the current session, call the `queue.identify()`
	without parameters.
	To connect to the existing session, call the `queue.identify(session_uuid)`
	with the UUID of the session.
	In case of attempt to use an invalid format UUID or expired UUID, an error will
	be thrown.
	Usage example:
	Sometimes we need an ability to acknowledge a task after reconnect (because
	retrying it is undesirable) or even acknowlegde using another connection.
	Example of code for connecting to the old session in case of reconnection:
	```lua
	local netbox = require('net.box')
	local conn = netbox.connect('localhost:1918', { reconnect_after = 5 })
	local session_uuid = conn:call('queue.identify')
	conn:on_connect(function()
	conn:call('queue.identify', {session_uuid})
	end)
	```