Update readme

Fix invalid language's bug

Fix typo

Fix upgrade bug. Add time remaining in upgrading. Close xalanq#23

Fix race command: change countdown URL and open all problems of the c…

…ontest. Close xalanq#21

Update gif

Add the last submission info in ~/.cfsession. Close xalanq#10

Add a new command for opening submission's page. Close xalanq#10

Fix submit a unexpected file. Close xalanq#14

Fix parse bugs. Close xalanq#11, xalanq#12