Switch docs to Sphinx (#1166)

diff --git a/doc/requirements.txt b/doc/requirements.txt
new file mode 100644
index 0000000..8c261cd
--- /dev/null
+++ b/doc/requirements.txt
@@ -0,0 +1,5 @@
+dunamai
+furo
+sphinx
+sphinx-autobuild
+sphinx-copybutton