I wouldn't have read out the letter, but even if my Chairman had, I wouldn't be including any details from it in the minutes. "Chairman read a letter of resignation from Councillor X" End of story. It'll be forgotten within days.
One of my fellow Councillors issued a two-page resignation rant, largely aimed at me, and to ensure that it wasn't lost in abbreviated minute-taking, he sent about 50 copies to local individuals, organisations, neighbouring parish councils, district council officers and members, county council officers and members, the local association, ACRE, Fields in Trust, funders... Oh how we laughed! I never did manage to clarify whether the Queen, the Prime Minister or the Archbishop of Canterbury received one!!