Moderate recommendation to escape '(' in doc strings

Thanks to 57e2ca5c and related changes, opening brackets at the
leftmost column inside doc strings are no longer mistaken for the
start of a defun.

* doc/lispref/tips.texi (Documentation Tips): Clarify recommendation
and move it down the list.
* etc/NEWS: Announce.
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passed #4906
test-all

00:54:42