BufReader: document internal functions

library/std/src/io/buffered/bufreader/buffer.rs

@@ -97,6 +97,7 @@ impl Buffer {
         self.pos = self.pos.saturating_sub(amt);
     }
 
+    /// Read more bytes into the buffer without discarding any of its contents
     pub fn read_more(&mut self, mut reader: impl Read) -> io::Result<()> {
         let mut buf = BorrowedBuf::from(&mut self.buf[self.pos..]);
         let old_init = self.initialized - self.pos;
@@ -109,6 +110,7 @@ impl Buffer {
         Ok(())
     }
 
+    /// Remove bytes that have already been read from the buffer.
     pub fn backshift(&mut self) {
         self.buf.copy_within(self.pos.., 0);
         self.initialized -= self.pos;