Set up new repository and add README, license, etc files

This used to be a gh-pages branch of the main MacVim repository. We have
now moved to a separate repository
(https://github.com/macvim-dev/macvim-dev.github.io) which allows us to
serve the page from the root org level, and also allow us to nest the
docs project within it so that we can host/build the docs pages
independently and still have the URL work in a relative fashion to this
page (https://macvim-dev.github.io/docs and https://macvim.org/docs).

The old branch will have a new meta-tag redirect to point to this site
(GitHub Pages doesn't support generic server-side 3xx status code
redirect).

Author: ychin

.github/FUNDING.yml

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+github: macvim-dev
+open_collective: macvim

LICENSE

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+MIT License
+
+Copyright (c) 2023 MacVim developers
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+## MacVim website
+
+This is the repository for MacVim's website (https://macvim.org). It is hosted using GitHub Pages on a custom domain. Note that the generated documentation (https://macvim.org/docs) is hosted on a separate repository (https://github.com/macvim-dev/docs), which works because GitHub Pages automatically set up custom domain redirects for individual projects if the root organization page has a custom domain.
+
+This site is also used by the builtin Sparkle updater as it uses https://macvim.org/appcast/latest.xml for information for the latest update.
+