Fix typo.

This is useful **is** you have -> This is useful **if** you have

1 files changed, 1 insertions, 1 deletions

diff --git a/README.md b/README.md
index 2cdb936..2effc06 100644
--- a/README.md
+++ b/README.md
@@ -83,7 +83,7 @@ fastdom.write(function() {
 
 ### FastDom#defer([frames,] callback[, context])
 
-Defers a job for the number of frames specified. This is useful is you have a particualrly expensive piece of work to do, and don't want it to be done with all the other work.
+Defers a job for the number of frames specified. This is useful if you have a particualrly expensive piece of work to do, and don't want it to be done with all the other work.
 
 For example; you are using third party library that doesn't expose an API that allows you split DOM read/write work, `fastdom.defer()` will push this work futher into the future and prevent it from disrupting other carefully batched work.