pw_sys_io: Doxygenify TryReadByte()

Change-Id: Ied2e1004d22e62714d32cd308848c178fe4ff89c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/153190
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Kayce Basques <kayce@google.com>
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Kayce Basques <kayce@google.com>

pw_sys_io/docs.rst

@@ -42,6 +42,7 @@ implementation.
 API reference
 =============
 .. doxygenfunction:: pw::sys_io::ReadByte(std::byte* dest)
+.. doxygenfunction:: pw::sys_io::TryReadByte(std::byte* dest)
 
 Dependencies
 ============

pw_sys_io/public/pw_sys_io/sys_io.h

@@ -54,16 +54,20 @@ namespace pw::sys_io {
 /// @warning Do not build production projects on top of `pw_sys_io`.
 ///
 /// @returns
-/// * @pw_status{OK} - A byte was successfully read.
+/// * @pw_status{OK} - A byte was successfully read and is in `dest`.
 /// * @pw_status{RESOURCE_EXHAUSTED} - The underlying source vanished.
 Status ReadByte(std::byte* dest);
 
-// Read a single byte from the sys io backend, if available.
-// Implemented by: Backend
-//
-// Returns OkStatus() - A byte was successfully read, and is in dest.
-// Status::Unavailable() - No byte is available to read; try later.
-// Status::Unimplemented() - Not supported on this target.
+/// Reads a single byte from the `pw_sys_io` backend, if available.
+///
+/// @pre This function must be implemented by the `pw_sys_io` backend.
+///
+/// @warning Do not build production projects on top of `pw_sys_io`.
+///
+/// @returns
+/// * @pw_status{OK} - A byte was successfully read and is in `dest`.
+/// * @pw_status{UNAVAILABLE} - No byte is available to read; try later.
+/// * @pw_status{UNIMPLEMENTED} - The function is not supported on this target.
 Status TryReadByte(std::byte* dest);
 
 // Write a single byte out the sys io backend.