selenium: fix SQLShare link in README.md

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
selenium: more improvements to README

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
selenium: improve login_to_sqlshare.py

Fix a comment
Use the Keys class instead of '\r\n' for special characters

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>