Fix readthedocs runner (#2230)

* The new build system requires a requirements.txt

* .txt is in .gitignore, had to force it in

1 files changed, 1 insertions, 0 deletions

diff --git a/docs/requirements.txt b/docs/requirements.txt
new file mode 100644
index 00000000..52b04f2e
--- /dev/null
+++ b/docs/requirements.txt
@@ -0,0 +1 @@
+sphinx_rtd_theme
\ No newline at end of file