[3.10] Improve documentation for adding datetime and timedelta (gh-93267)

[miss-islington]

(cherry picked from commit 6e44bf9)

Co-authored-by: BenjaminHelyer [email protected]

• Issue: Wrong Result Documented in Date Arithmetic datetime #93267

[miss-islington]

@BenjaminHelyer and @ericvsmith: Status check is done, and it's a failure ❌ .

[miss-islington]

@BenjaminHelyer and @ericvsmith: Status check is done, and it's a failure ❌ .

[miss-islington]

Status check is done, and it's a success ✅ .