database/sql: improve the documentation of Conn.Raw
database/sql: improve the documentation of Conn.Raw

Fixes #47500

Change-Id: Ibd44e4db15ea45bb53a6651a6567edfe6104d3d6
GitHub-Last-Rev: 61b8abbc28908fc807af7188e19089ac454b4817
GitHub-Pull-Request: golang/go#47503
Reviewed-on: https://go-review.googlesource.com/c/go/+/338970
Reviewed-by: Daniel Theophanes <14db39248b80c6688f7e9808ba5055f2e56426f3@gmail.com>
Trust: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

CAFxX/go,cloudflare/go,CAFxX/go,cloudflare/go,golang/go,cloudflare/go,golang/go,golang/go,nawawi/go,golang/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,golang/go,golang/go,nawawi/go,nawawi/go,nawawi/go,CAFxX/go,cloudflare/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,CAFxX/go,nawawi/go,cloudflare/go,nawawi/go,CAFxX/go,CAFxX/go,cloudflare/go