sbi-rt: small fix on documents

Signed-off-by: Zhouqi Jiang <luojia@hust.edu.cn>

sbi-rt/src/binary.rs

@@ -1,4 +1,4 @@
-//! Capture 3. Binary Encoding
+//! Chapter 3. Binary Encoding
 
 use sbi_spec::binary::SbiRet;