Fixed a typo in example

Author: willmcgugan

README.md

@@ -12,7 +12,7 @@ same way as any other supported filesystem.
 Open an S3FS by explicitly using the constructor:
 
 ```python
-from s3_s3fs import s3FS
+from s3_s3fs import S3FS
 s3fs = S3FS('mybucket')
 ```