Add renderer for Sphinx .rst files, for user manual previews

Ref infrastructure/blender-projects-platform#51

Pull Request: https://projects.blender.org/infrastructure/gitea-custom/pulls/2

sphinx/README.md

@@ -0,0 +1,28 @@
+# Sphinx RST to HTML Preview
+
+Command for generating previews of RST files on projects.blender.org.
+
+The template is adapted from the Blender manual to support the same extensions.
+
+### Deployment
+
+Install dependencies.
+
+    pip3 install -r requirements.txt
+
+Add to Gitea app.ini.
+
+    [markup.restructuredtext]
+    ENABLED = true
+    FILE_EXTENSIONS = .rst
+    RENDER_COMMAND = "timeout 30s ./custom/sphinx/sphinx_to_html.py --user sphinx --user-work-dir /path/to/dir"
+    IS_INPUT_FILE = true
+
+    [repository.editor]
+    LINE_WRAP_EXTENSIONS = .txt,.md,.markdown,.mdown,.mkd,.rst
+    PREVIEWABLE_FILE_MODES = markdown,restructuredtext
+
+The `sphinx` user is required for sandboxing of sphinx-build which we do not
+assume to be secure. The work directory should be writable by both the gitea
+user and sphinx user, with the sphinx user having as little access as possible
+to other directories.