Summary:
Our query parsing, planning and execution architecture was described on
Phabricator wiki pages, Phriction. This commit copies the said
documentation here, so that it's easier to access for all developers.
Additional benefit is tracking the changes and hopefully suggesting to
developers to keep it up to date.
Besides making a copy, the documentation has been updated to reflect the
current state of the codebase. Note that some things are still missing,
but what was written should now be correct.
Reviewers: mtomic, llugovic
Reviewed By: mtomic
Subscribers: pullbot
Differential Revision: https://phabricator.memgraph.io/D1854
