Add Docusaurus documentation website

Summary:
Sets up a [Docusaurus](https://docusaurus.io/) site under `cinderx/website/` that builds the public CinderX documentation and publishes it to GitHub Pages at https://facebookincubator.github.io/cinderx/.

Migrates the existing developer docs out of `Docs/` (`.rst`/`.md`) and `Jit/` into `website/docs/` as Markdown, organized into JIT Compiler, Static Python, and Strict Modules sections with a hand-authored sidebar (`sidebars.ts`). Any internal docs have been moved into the other internal folder. The docs plugin serves pages at the site root, parses `.md` as CommonMark to avoid MDX surprises, and fails the build on broken internal links so doc rot is caught in CI.

Adds the `.github/workflows/docs.yml` GitHub Actions workflow to build the site on pull requests touching `cinderx/website/` and deploy to GitHub Pages when those changes land on `main`. Updates the top-level OSS `README.md` to link to the published documentation site. The `website/README.md` documents the layout and how to add or edit pages.

open questions:
1. can we purchase the cinderx.com or .org domain name so we dont have to use the github.io url?
2. what do we think about moving the docs into the website folder rather than a top level folder? this is the standard way to organise it with docusaurus
3. I think the performance section is interesting enough to be a page on its own, but for now as we don't have a lot of data I just added it to the intro page (uses the latest stats from the pycon talk)

Reviewed By: DinoV, yangdanny97

Differential Revision: D109353395

fbshipit-source-id: f4802f9f69b0be9b87ea7e925c3639e88fc9a06f

Author: javabster

.github/workflows/docs.yml

@@ -0,0 +1,69 @@
+name: Documentation
+
+on:
+  # Deploy when docs or the website change on main.
+  push:
+    branches: [main]
+    paths:
+      - 'cinderx/website/**'
+  # Build-only check on PRs that touch docs.
+  pull_request:
+    paths:
+      - 'cinderx/website/**'
+  # Allow manual runs.
+  workflow_dispatch:
+
+# Allow the deploy job to publish to GitHub Pages via OIDC.
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Only one concurrent deploy; don't cancel an in-progress production deploy.
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build:
+    if: github.repository == 'facebookincubator/cinderx'
+    name: Build site
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: cinderx/website
+    steps:
+      - name: Checkout CinderX
+        uses: actions/checkout@v6
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: yarn
+          cache-dependency-path: cinderx/website/yarn.lock
+
+      - name: Install dependencies
+        run: yarn install --frozen-lockfile
+
+      - name: Build (fails on broken links)
+        run: yarn build
+
+      - name: Upload Pages artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: cinderx/website/build
+
+  deploy:
+    # Only deploy from main; PRs run the build job above as a check.
+    if: github.repository == 'facebookincubator/cinderx' && github.event_name != 'pull_request'
+    name: Deploy to GitHub Pages
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy
+        id: deployment
+        uses: actions/deploy-pages@v4

README.md

@@ -54,7 +54,9 @@ This will configure the CinderX extension to automatically compile Python
 functions to machine code.  It will track what functions are called frequently
 and compile the hottest ones automatically.
 
-See [the JIT README](cinderx/Jit/README.md) for more details.
+See [the JIT documentation](https://facebookincubator.github.io/cinderx/docs/jit) for
+more details, or browse the full [CinderX documentation
+site](https://facebookincubator.github.io/cinderx/).
 
 ## CinderX vs Cinder