IF ADOPTED: steps identified if the specification is adopted

If this proposal is adopted:

[x] this repository should be transferred to: https://github.com/FDSN/miniSEED3
[x] the link to download the Extra Headers JSON Schema file in fdsn-reserved.rst should be updated to reflect the new location.
[x] update links to software in software.rst from "iris-edu" to "EarthScope"
[x] remove DRAFT markings in conf.py, 2 places: release string and sphinxmark_enable boolean.
[x] update readthedocs project to new repository location and configure for export via https://docs.fdsn.org/projects/miniseed3/
[x] update project URL on main repo Code page to https://docs.fdsn.org/projects/miniseed3/
[x] add initial release entry to changes.rst
[x] add project to the base https://docs.fdsn.org/ page
[x] add miniSEED 3 entry to https://fdsn.org/publications/

FDSN / miniSEED3