fix typo in README.md

Line 5 had a superfluous "in" between "used" and "on."  This change removes the "in" to improve the clarity of the sentence.  No other changes were made.

Before: ...can be used in on the same element...
After: ...can be used on the same element...
Merge pull request #3 from lpappone/patch-1

Fix typo in README.