Fixed typo in README.md

README.md

@@ -178,7 +178,7 @@ switch_sides_pre(From,To) :- at(boat,From), side(From), side(To),
 ***
 
 *To unload an object in one of the sides of the river, the object has to
-be loaded into the boat and the boa has to be at that side*:
+be loaded into the boat and the boat has to be at that side*:
 
 ```
 unload_pre(Side,What) :- at(boat,Side), side(Side), loaded(What)