doc detail in gen as suggested

Co-authored-by: Travis Scrimshaw <[email protected]>

Author: fchapoton

src/sage/algebras/free_algebra_quotient.py

@@ -213,7 +213,7 @@ def _repr_(self) -> str:
 
     def gen(self, i):
         """
-        Return the i-th generator of the algebra.
+        Return the ``i``-th generator of the algebra.
 
         EXAMPLES::