fix the readthedocs build, enable readthedocs PR builds and move readthedocs config into .readthedocs.yml

[twisted-trac]

	@graingert reported
Trac ID	trac#9980
Type	release blocker: release process bug
Created	2020-09-27 10:42:39Z

the readthedocs builds are currently failing due to a py2 syntax error https://readthedocs.org/projects/twisted/builds/11964760/

steps that are needed:

go here: https://readthedocs.org/dashboard/twisted/advanced/#id_external_builds_enabled and tick this box
https://user-images.githubusercontent.com/413772/94362678-f6395d80-00b4-11eb-875a-3c0fd040fe55.png

then screenshot the "Default settings" fromset, it should look something like this: https://user-images.githubusercontent.com/413772/94362748-6f38b500-00b5-11eb-879b-ae7a067660f8.png I can use that to create a .readthedocs.yml file

I can then update the CI builder to use python 3.8 to create docs

then go here https://readthedocs.org/dashboard/twisted/integrations/create/ to double check the webhook is enabled https://i.imgflip.com/4gfv14.jpg

Searchable metadata

trac-id__9980 9980
type__release_blocker__release_process_bug release blocker: release process bug
reporter__graingert graingert
priority__highest highest
milestone__Python_3_x Python-3.x
branch__ 
branch_author__ 
status__closed closed
resolution__fixed fixed
component__core core
keywords__None None
time__1601203359836780 1601203359836780
changetime__1601749663548030 1601749663548030
version__None None
owner__glyph glyph
cc__graingert

[twisted-trac]

	@graingert set owner to @glyph

[twisted-trac]

	@graingert commented

this is a release blocker because the readthedocs builds are currently failing due to a py2 syntax error ​https://readthedocs.org/projects/twisted/builds/11964760/

[twisted-trac]

	@glyph commented

Sounds like a release process bug to me.

[twisted-trac]

	@graingert commented

If you can't get the oauth app working you can work around it by manually fixing the webhook: https://i.imgflip.com/4go3nq.jpg

[twisted-trac]

	@graingert commented

#1409 is passing on rtd!

[twisted-trac]

	@adiroiban set status to closed

In changeset 64d453e

#!CommitTicketReference repository="" revision="64d453e159dc3b9e54fe1f9b2ce9d9f505ed2cce"
Merge pull request #1409 from graingert/readthedocs-yml

Author: graingert 
Reviewer: adiroiban
Fixes: ticket:9980

Fix Read the docs build and enable building it at PR.