docs: reconfigure libbpf documentation syncing

This adds documentation files, including ones for autogenerating API
documentation based on code comments in the source code that's pulled
in via the mirror.

Signed-off-by: Grant Seltzer <grantseltzer@gmail.com>

.readthedocs.yaml

@@ -0,0 +1,17 @@
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+  builder: html
+  configuration: docs/conf.py
+
+# Optionally set the version of Python and requirements required to build your docs
+python:
+   version: 3.7
+   install:
+   - requirements: docs/sphinx/requirements.txt