DOC: improve the wording in CONTRIBUTING about how to document a bug fix

Insufficiently described bug fixes are still too frequent. It's a real
pain to create each new maintenance release, as 3/4 of the time is spent
trying to guess what problem a patch fixes, which is already important
in order to decide whether to pick the fix or not, but is even more
capital in order to write understandable release notes.

Christopher rightfully demands that a patch tagged "BUG" MUST ABSOLUTELY
describe the problem and why this problem is a bug. Describing the fix
is one thing but if the bug is unknown, why would there be a fix ? How
can a stable maintainer be convinced to take a fix if its author didn't
care about checking whether it was a real bug ? This patch tries to
explain a bit better what really needs to appear in the commit message
and how to describe a bug.

To be backported to all relevant stable versions.

(cherry picked from commit 41f638c1eb8167bb473a6c8811d7fd70d7c06e07)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
1 file changed