Blender Git Loki

API doc: info_gotcha: extend description of issues related to memory changes.

* Added a TL;DR first paragraph summarizing that one shall not keep any
reference to Blender data when modifying its container.

* Added some info about fact that adding items to some data containers
(like Collection) can also invalidate existing items (due to array
re-allocation).

* Added a Do/Don't example which shows a crash after adding some items
to a collection.

Related to T61297.