Change README files in both XSBench -cl and -amp

[ztschir]

Add the additional two contributors to the README files for both xsbench-cl and xsbench-amp.

Reference change in original source:
ANL-CESAR/XSBench@90e1332

[ztschir]

Decided to only change xsbench-amp, since xsbench-cl is on version 10 and the README should reflect this. Just adding the two additional names may not reflect what the author intended.

Refer to commit: 11a3ddb