markdownlint: allow break HTML

Github markdown only allows the `<br>` tag to be used in a table to
force a newline (there is otherwise no standard).  Allow this in the
markdownlint config.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I4d48352c678018d12aab3c1c9ec4c9e7eb1cbb42
diff --git a/config/markdownlint.yaml b/config/markdownlint.yaml
index dae3799..8783ec6 100644
--- a/config/markdownlint.yaml
+++ b/config/markdownlint.yaml
@@ -2,3 +2,5 @@
 MD013: false
 MD024:
     siblings_only: true
+MD033:
+    allowed_elements: ["br"]