Add $title-strong-weight and $title-strong-color variables to docs (#1100)

docs/documentation/elements/title.html

@@ -10,6 +10,10 @@ variables:
   value: $size-3
 - name: $title-weight
   value: $weight-semibold
+- name: $title-strong-weight
+  value: inherit
+- name: $title-strong-color
+  value: inherit
 - name: $subtitle-color
   value: $grey-dark
 - name: $subtitle-size