pw_sys_io: Doxygenify ReadBytes()

Change-Id: I1c5b7eb70a84e3a98ac45b2ab2884915ec0a2e84
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/154192
Reviewed-by: Kayce Basques <kayce@google.com>
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Kayce Basques <kayce@google.com>

pw_sys_io/docs.rst

@@ -45,6 +45,7 @@ API reference
 .. doxygenfunction:: pw::sys_io::TryReadByte(std::byte* dest)
 .. doxygenfunction:: pw::sys_io::WriteByte(std::byte b)
 .. doxygenfunction:: pw::sys_io::WriteLine(const std::string_view& s)
+.. doxygenfunction:: pw::sys_io::ReadBytes(ByteSpan dest)
 
 Dependencies
 ============

pw_sys_io/public/pw_sys_io/sys_io.h

@@ -97,18 +97,20 @@ Status WriteByte(std::byte b);
 ///   returned as part of the `StatusWithSize`.
 StatusWithSize WriteLine(const std::string_view& s);
 
-// Fill a byte span from the sys io backend using ReadByte().
-// Implemented by: Facade
-//
-// This function is implemented by this facade and simply uses ReadByte() to
-// read enough bytes to fill the destination span. If there's an error reading a
-// byte, the read is aborted and the contents of the destination span are
-// undefined. This function blocks until either an error occurs, or all bytes
-// are successfully read from the backend's ReadByte() implementation.
-//
-// Return status is OkStatus() if the destination span was successfully
-// filled. In all cases, the number of bytes successuflly read to the
-// destination span are returned as part of the StatusWithSize.
+/// Fills a byte span from the `pw_sys_io` backend using `ReadByte()`.
+///
+/// @pre This function must be implemented by the `pw_sys_io` facade.
+///
+/// This function is implemented by the facade and simply uses `ReadByte()` to
+/// read enough bytes to fill the destination span. If there's an error reading
+/// a byte, the read is aborted and the contents of the destination span are
+/// undefined. This function blocks until either an error occurs or all bytes
+/// are successfully read from the backend's `ReadByte()` implementation.
+///
+/// @returns
+/// * @pw_status{OK} if the destination span was successfully filled. In all
+///   cases, the number of bytes successuflly read to the destination span are
+///   returned as part of the `StatusWithSize`.
 StatusWithSize ReadBytes(ByteSpan dest);
 
 // Write span of bytes out the sys io backend using WriteByte().