feat: doc/build, doc/install

Problem:
Currently, BUILD.md and INSTALL.md are only available on github.

Solution:
Copy them to `content/doc2/` and let Hugo render them.

Author: justinmk

README.md

@@ -8,12 +8,6 @@ This repository contains the source for the neovim.io website.
 
 Just fork this repository and send us a pull request! :-)
 
-To embed raw html:
-
-    {{< rawhtml >}}
-    <lol>
-    {{< /rawhtml >}}
-
 ## Setup
 
 This site is statically generated using Hugo. It takes one minute to get setup,
@@ -33,8 +27,11 @@ just do the following:
 
 Notes:
 
-- www.neovim.io/doc is served by https://github.com/neovim/doc (which previously
-  crawled neovim.io/doc2 generated from this repository).
+- Updating `content/doc2/` currently requires a human to run: `./sync_docs.sh`
+- Files in `content/doc2/` are synced to https://github.com/neovim/doc/ by
+  [this CI job](https://github.com/neovim/doc/blob/4ab2e06af98dadbd35c4282c1b18304d87f8eb59/ci/doc-index.sh#L10-L13).
+    - This is because `neovim.io/doc/` is served by https://github.com/neovim/doc/
+      (where the user documentation HTML is published).
 - Site search (for `:help` docs) is served by [Algolia Docsearch](https://docsearch.algolia.com/).
     - The javascript and UI container were setup in [this commit](https://github.com/neovim/neovim.github.io/commit/ce9aef12eb1c98135965e3a9c5c792bf9e506a76).
     - The docs pages don't use the layout so they also need to [manually include](https://github.com/neovim/neovim/pull/23839) the javascript and define a UI container.

content/community.md

@@ -1,7 +1,7 @@
 ---
 title: Documentation
 active: Documentation
-type: default
+layout: single
 ---
 
 <section class="front-section">

content/doc2/index.html renamed to content/doc2/_index.html

@@ -0,0 +1,40 @@
+#!/bin/bash
+
+# This script syncs files from Neovim core, to content/doc2/:
+# - BUILD.md
+# - INSTALL.md
+#
+# After Hugo publishes the rendered HTML from content/doc2/, the files are
+# later copied from doc2/ to doc/ by this CI task:
+# https://github.com/neovim/doc/blob/main/ci/doc-index.sh
+
+set -eu
+
+# Add Hugo markdown header.
+add_frontmatter() {
+  local file="$1"
+  local title="$2"
+
+  cat > "$file.tmp" <<EOF
+---
+title: $title
+type: page
+---
+
+EOF
+  cat "$file" >> "$file.tmp"
+  mv "$file.tmp" "$file"
+}
+
+curl -Lo content/doc2/build.md https://raw.githubusercontent.com/neovim/neovim/refs/heads/master/BUILD.md
+add_frontmatter content/doc2/build.md "Build"
+# Replace INSTALL.md hyperlinks with "./install".
+sed -i '' 's/INSTALL\.md/\.\.\/install/g' content/doc2/build.md
+
+curl -Lo content/doc2/install.md https://raw.githubusercontent.com/neovim/neovim/refs/heads/master/INSTALL.md
+add_frontmatter content/doc2/install.md "Install"
+# Replace BUILD.md hyperlinks with "./build".
+sed -i '' 's/BUILD\.md/\.\.\/build/g' content/doc2/install.md
+
+git add content/doc2/
+git commit -m 'update content/doc2/ files from neovim/neovim repo'