sha1-checked: fix typo in docs (#583)

sha1-checked/README.md

@@ -18,7 +18,8 @@ unsuitable for further use in any security critical capacity, as it is
 But, this crate provides the detection [algorithm] pioneered by git, to detect hash collisions when they
 occur and prevent them. The [paper] has more details on how this works.
 
-This implementation will be slower to use than the pure SHA-1 implementation, as more work as to be done.
+This implementation will be slower to use than the pure SHA-1 implementation, as it has to do more computations and
+it can not rely on hardware acceleration available on some CPUs.
 
 ## Examples