[DOCS] CREATE_REPLICATION_SLOT exported snapshot

Hi, There's a brief mention of CREATE_REPLICATION_SLOT exporting a snapshot here: https://www.postgresql.org/docs/devel/static/logicaldecoding-explanation.html#AEN71570 but how to access the snapshot identifier is not documented anywhere. So I came up with the attached patch (against master

[DOCS] Suggestion - Document a currently undocumented(?) feature - SELECT Table FROM Table

Hello, wonderful people who are providing us with a wonderful piece of software! Just wanted to suggest that an existing feature is included in the documentation. It seems to be undocumented now. Also I don't think it's an obvious feature. I looked carefully under the reference section for SELECT,