Change slithtly -> slightly in README.md

Author: alexandercampbell

src/doc/intro.md

@@ -510,10 +510,10 @@ numbers[1] is 3
 numbers[0] is 2
 ```
 
-Each time, we can get a slithtly different output because the threads
-are not quaranteed to run in any set order. If you get the same order
-every time it is because each of these threads are very small and
-complete too fast for their indeterminate behavior to surface.
+Each time, we can get a slightly different output because the threads are not
+quaranteed to run in any set order. If you get the same order every time it is
+because each of these threads are very small and complete too fast for their
+indeterminate behavior to surface.
 
 The important part here is that the Rust compiler was able to use ownership to
 give us assurance _at compile time_ that we weren't doing something incorrect