doc: truncate 'close' event descriptions for fs.ReadStream and fs.WriteStream
Per suggestion from @mscdex in PR #15790
Checklist
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documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
doc
As with PR #15790, I tried to follow the commit message guidelines but I couldn't think any of good message that was 50 characters or less. If anyone has recommendations, I'd be happy to update it.