Add .readthedocs.yaml config and docs/requirements.txt

ReadTheDocs now requires a .readthedocs.yaml file at the repo root.
Also adds docs/requirements.txt with Sphinx and alabaster so the RTD
build environment has all needed dependencies.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: derek73

.readthedocs.yaml

@@ -0,0 +1,15 @@
+version: 2
+
+build:
+  os: ubuntu-24.04
+  tools:
+    python: "3.12"
+
+sphinx:
+  configuration: docs/conf.py
+
+python:
+  install:
+    - method: pip
+      path: .
+    - requirements: docs/requirements.txt

docs/requirements.txt

@@ -0,0 +1,2 @@
+Sphinx
+alabaster