markdownlint: update from openbmc-build-scripts reference

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I3d3dfb24e571eaa43b5c2d4b423dcca7cba88d74
diff --git a/.markdownlint.yaml b/.markdownlint.yaml
index 15c9e81..bcc4833 100644
--- a/.markdownlint.yaml
+++ b/.markdownlint.yaml
@@ -1,3 +1,6 @@
 default: true
+MD013: false
 MD024:
     siblings_only: true
+MD033:
+    allowed_elements: ["br", "sub", "sup"]