modify readme.txt.
modify readme.txt.
hifive-snu/hifive-test-explorer,hifive-snu/hifive-test-explorer,hifive-snu/hifive-test-explorer,hifive/hifive-pitalium-explorer,hifive/hifive-test-explorer,hifive/hifive-pitalium-explorer,hifive/hifive-pitalium-explorer,hifive-snu/hifive-test-explorer,hifive/hifive-test-explorer,hifive/hifive-test-explorer,hifive/hifive-test-explorer,hifive/hifive-pitalium-explorer