#20135: FAQ entry for list mutation.  (See also 6375bf34fff6.)

I accidentally committed this in 6375bf34fff6; this changeset addresses the
last review comments on the patch.

This is a perennial question and something someone opens a ticket for probably
every other month or so, so I'm surprised we didn't already have a FAQ entry
for it.

The original patch was written by M. Votz, refined first by Ezio Melotti and
further refined by me.

--HG--
branch : 3.4
cleanup overflowing handling in unicode_decode_call_errorhandler and unicode_encode_ucs1 (closes #22518)

--HG--
branch : 3.3
extra : source : b2e68274aa8ebfba676d6d40fe69ac68519e2022
NEWS issue for #22518

--HG--
branch : 3.3
extra : amend_source : 2c57943366dd265713a3ab41b9b427271eb4c7ee
merge 3.3 (closes #22518)

--HG--
branch : 3.4
fix overflow checking in PyBytes_Repr (closes #22519)

--HG--
branch : 3.3
extra : source : d9cd11eda1521790b89c210ddb1cba28cd05c9fa
extra : amend_source : 4cba45b1132194e95abe3592b2a1f0eec0de43ab
merge 3.3 (closes #22519)

--HG--
branch : 3.4
these variables ought to be Py_ssize_t

--HG--
branch : 3.3
merge 3.3

--HG--
branch : 3.4