feat(docs): add markdown linter for exercises README.md files

exercises/options/README.md

@@ -1,7 +1,8 @@
 # Options
 
-Type Option represents an optional value: every Option is either Some and contains a value, or None, and does not. 
+Type Option represents an optional value: every Option is either Some and contains a value, or None, and does not.
 Option types are very common in Rust code, as they have a number of uses:
+
 - Initial values
 - Return values for functions that are not defined over their entire input range (partial functions)
 - Return value for otherwise reporting simple errors, where None is returned on error