chore: add section for PR ownership to maintainers guide (#2674)

Signed-off-by: ldetmer <[email protected]>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: ldetmer

doc/library-maintainer-guide.md

@@ -1,14 +1,12 @@
 # Library Maintainer Guide
 
-This guide is aimed at maintainers of libraries using Librarian, where the
-library contains hand-written code. (Fully-generated libraries are automated
-for both generation and release.)
-
 This guide is task-oriented, specifically for core/handwritten/hybrid library
 maintainers. See the
 [generated CLI documentation](https://pkg.go.dev/github.com/googleapis/librarian/cmd/librarian)
 for a more comprehensive list of commands and flags.
 
+For libraries onboarded to automation, please see [automation section below](#using-automated-releases).
+
 This guide uses the term Librarian (capital L, regular font) for the overall
 Librarian system, and `librarian` (lower case L, code font) for the CLI.
 
@@ -293,3 +291,13 @@ future readers.
 Create a PR with the configuration change, get it reviewed and merged, and
 the next time release automation runs against the repository, it will consider
 the library eligible for automatic releases.
+
+### Ownership of PRs once onboarded to automation
+
+Once a library is onboarded to Librarian automation, the Librarian team is
+responsible for approving and merging PRs generated by Librarian. Maintainers are
+not expected to be involved in this process, unless PR checks fail.  In that
+case a ticket will be opened up in the repository and needs to be addressed by
+Maintainers.  This can potentially block generation/release until issue has been 
+resolved.
+