Solution for Raku/doc/issues/1246

This PR proposes a solution to Raku/doc/issues/1246.  (I now realize
that issue was in the doc repo rather than the problem-solving one and
thus _technically_ I should open an issue in this repo and discuss the
matter here before opening a PR.  Since that issue has been active for
5 years and has generated the a similar discussion as it would have as
a problem-solving issue, I believe it can stand in for an issue in
this repo.  But if anyone objects, I can close this PR and do this
more by the book.)

Specifically, this PR would allow alternate documentation frontends
such as the [one prepared by
@Altai-man](https://github.com/Altai-man/docs.raku.org) to have a home
on the raku.org website (at `docs.$new-site-name.raku.org`).  It would
also provide a list of all such alternate frontends, some guidance
about creating new ones, and a note that an alternate frontend could
one day become the new primary doc site.  Please see the solution
document for full details.

solutions/documentation/new-documentation-frontends.md

@@ -0,0 +1,79 @@
+# Solution – Multiple docs websites
+
+Allow anyone to set up an alternate frontend for the Raku documentation and
+serve that frontend via a raku.org subdomain so long as it is built from the
+raku/doc source.
+
+## Details
+
+The first section of the raku/doc README currently reads:
+
+```md
+# Official Documentation of Raku™
+
+[![artistic](https://img.shields.io/badge/license-Artistic%202.0-blue.svg?style=flat)](https://opensource.org/licenses/Artistic-2.0)
+[![CircleCI](https://circleci.com/gh/Raku/doc/tree/master.svg?style=svg)](https://circleci.com/gh/Raku/doc/tree/master)
+[![test](https://github.com/Raku/doc/actions/workflows/test.yml/badge.svg)](https://github.com/Raku/doc/actions/workflows/test.yml)
+
+An HTML version of this documentation can be found
+at [https://docs.raku.org/](https://docs.raku.org/) and also
+at [`rakudocs.github.io`](https://rakudocs.github.io) (which is
+actually updated more frequently).
+This is currently the recommended way to consume the documentation.
+```
+
+This solution document calls for it being changed to:
+
+
+```md
+# Official Documentation of Raku™
+
+[![artistic](https://img.shields.io/badge/license-Artistic%202.0-blue.svg?style=flat)](https://opensource.org/licenses/Artistic-2.0)
+[![CircleCI](https://circleci.com/gh/Raku/doc/tree/master.svg?style=svg)](https://circleci.com/gh/Raku/doc/tree/master)
+[![test](https://github.com/Raku/doc/actions/workflows/test.yml/badge.svg)](https://github.com/Raku/doc/actions/workflows/test.yml)
+
+This repo contains the source code of the Raku documentation.  The official
+version HTML version of this documentation can be found
+at [https://docs.raku.org/](https://docs.raku.org/), which is
+currently the recommended way to consume the documentation.  Alternate versions
+of the documentation can be found at:
+
+   * docs.preview.raku.org – updated more frequently
+
+If you would like to add your own alternate version to this list, please submit
+a PR as described in the [`CONTRIBUTING`](/CONTRIBUTING.md#Adding-an-alternate-version).
+
+```
+
+(`docs.preview.org` should proxy to the site currently at `rakudocs.github.io`.)
+
+And add the following section to `CONTRIBUTING.md`:
+
+```md
+## Adding an alternate version
+
+Anyone can submit an alternate frontend for the Raku documentation so long as it
+is built from the source in this repo.  To do so, please submit a PR with the
+name of your site and the base URL at which it is avalible.  Once that PR is
+merged, the URL `docs.$your-site-name.raku.org` will proxy to your site and your
+site will
+
+To add your own presentation of the documentation in this repo, please submit a
+PR with the name of your site and its base URL.  When merged,
+`docs.$your-site-name.raku.org` will mirror to your site and your site will be
+added to the list in the `README` for this repo.
+
+While it's not necessary for your site to render *all* of the content from this
+repo, it should probably render a large fraction – if it doesn't, it might make
+sense for your site to be a seperate Raku resouce rather than an alternate
+documentation site.  Similarly, your site should not use any non-minimal amount
+of content that is *not* in this repo (though it's fine for you to submit PRs to
+this repo that your version will render but others will not).  The purpose
+behind both of these restrictions is to prevent fragmentation of the effort that
+goes into maintaing the Raku documentation's _source_ while still allowing
+experimentation in the documentation's _presentation_.
+
+If an alternate version of the documentation gains enough widespread aproval in
+the Raku community, that version may be promoted to the official version.  If
+so, the current official version will be made avalible as an alternate version.
+```