IVGCVSW-3600 Update the docs with the naming convention for dynamic backend files
IVGCVSW-3600 Update the docs with the naming convention for dynamic
backend files

 * Added a section to the backends' README file to detail the
   dynamic backend file naming scheme
 * Added table with examples of valid/not valid filenames

Signed-off-by: Matteo Martincigh <c6d77cbcee86d63acbf5236b8a439153c50030ae@arm.com>
Change-Id: I59b88b96292a189056b9fceb155aedd07ee27225

ARM-software/armnn,ARM-software/armnn,ARM-software/armnn