[bsp][stm32 bluepill] 更新readme
[bsp][stm32 bluepill] 更新readme

hezlog/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,hezlog/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread,hezlog/rt-thread,hezlog/rt-thread,hezlog/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread