Update README.md

Author: chyyuu

README.md

@@ -4,7 +4,7 @@ ucore os labs was used as OS Experiments in OS Course Of Dept. of Computer Scien
 
 NEWS
 ====
-- 2019.03.01: [step_by_step rcore os labs from zero](https://github.com/LearningOS/rcore_step_by_step) is in progress. Thanks Qingling Pan, Fengyuan Liu's great work!
+- 2019.03.01: [step_by_step rcore os labs from scratch](https://github.com/LearningOS/rcore_step_by_step) is in progress. Thanks Qingling Pan, Fengyuan Liu's great work!
 - 2019.01.19: [rcore os labs(pre-alpha version)](https://github.com/oscourse-tsinghua/rcore_plus/tree/lab8-rv32) on RISC-V(32bit) were released. Thanks Runji Wang, Wei Zhang, Zhenyang Dai, Jiajie Chen, Yuekai Jia, Cheng Lu...'s great work!
 - 2019.01.19: [rcore os labs(pre-pre-alpha version)](https://github.com/oscourse-tsinghua/rcore_plus/tree/lab8-aarch64) on Raspberry Pi(AARCH 64bit) were released. Thanks Yuekai Jia, Runji Wang, Jiajie Chen...'s great work!
 - 2018.04.03：ucore os labs were ported on RISC-V(64bit) CPU（privileged arch spec 1.10). You can access [repo's riscv64-priv-1.10 branch](https://github.com/chyyuu/ucore_os_lab/tree/riscv64-priv-1.10). Thanks Zhengxing Shi's great work!