README doc updates

General editing, no siginficant content changes.
Updates to UPGRADING doc

* general editing
* renumbering
* changing rt3 references to rt4
* more information about SLA upgrade
Documentation updates to admin tutorial
Documentation updates for tutorial
Documentation updates for constituencies
A few nits after re-re-reading the docs updates.

I'm striking the reference to NIS in the mail section.
We started needing 4.0.6 sometime after UPGRADING was updated.
Document the problem with RTIR_DisableBlocksQueue recorded in #22308
Merge branch '2.9/doc-updates' into 2.9-trunk
MYMETA comes in json AND yaml.