cmd/staticcheck: improve wording for SA6003
Converting a string to a slice of runes before ranging over it
-You may want to loop over the runes in a string. As long as you are
-only interested in the runes, and not the indices, you can loop over
-the string itself, instead of converting it to a slice of runes first.
-That is,
+You may want to loop over the runes in a string. Instead of converting
+the string to a slice of runes and looping over that, you can loop
+over the string itself. That is,
```
for _, r := range s {}
