updated description of the create image screen

I update the current description on sceen
/project/images ->"Create Image" that it said:
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Specify an image to upload to the Image Service.
Currently only images available via an HTTP URL
are supported. The image location must be accessible
to the Image Service. Compressed image binaries are
supported (.zip and .tar.gz.)

Please note: The Image Location field MUST be a
valid and direct URL to the image binary. URLs that
redirect or serve error pages will result in unusable
images.
-------
Since horizon supports upload image from local file
system.
Closes-Bug: #1254273

Change-Id: I8bc706289f45f5f8c2db7ffa5e80b1f949a63867
Merge "updated description of the create image screen"