Add information about retrying on 429 error code

[hovaesco]

Description

Add information about retrying on 429 error code accordingly to trinodb/trino-python-client#455 (comment)

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# Section
* Fix some things. ({issue}`issuenumber`)

[hashhar]

LGTM. I'll let @electrum take a look before merging.

[mosabua]

Just some minimal formatting to fix, then good to go.

[electrum]

Suggested changes look good

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