Update Intro

doc/intro.md

@@ -2,5 +2,5 @@ A permutation is a rearrangement of the elements in an ordered collection. It
 is a one-to-one mapping—a bijection—and therefore reversible.
 [Lehmer codes](https://en.wikipedia.org/wiki/Lehmer_code) provide a mapping
 between positive integers and permutations, which make it possible to describe
-a permutation of _n_ elements in _O(nlog(n))_ space. _Metamorphose_ provides
+a permutation of _n_ elements in _O(nlog(n))_ space. __Metamorphose__  provides
 an implementation of this encoding.