git: aa26195de58d - stable/13 - sys/README.md: Add a section for documentation

The branch stable/13 has been updated by mhorne:

URL: https://cgit.FreeBSD.org/src/commit/?id=aa26195de58d6dc8e3d989ec50f1c5934c3f0e22

commit aa26195de58d6dc8e3d989ec50f1c5934c3f0e22
Author:     Mitchell Horne <mhorne@FreeBSD.org>
AuthorDate: 2023-08-03 13:48:17 +0000
Commit:     Mitchell Horne <mhorne@FreeBSD.org>
CommitDate: 2023-09-11 22:40:33 +0000

    sys/README.md: Add a section for documentation
    
    Add web links to intro(9) and the Architecture Handbook.
    
    Reviewed by:    lwhsu, emaste
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D41253
    
    (cherry picked from commit 32e47f62724e6cce2df0bc69d6ceba2d058d3585)
---
 sys/README.md | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/sys/README.md b/sys/README.md
index ad7ff9efa578..5836ade3deaa 100644
--- a/sys/README.md
+++ b/sys/README.md
@@ -9,6 +9,17 @@ architecture. `GENERIC` is the configuration used in release builds. `NOTES`
 contains documentation of all possible entries. `LINT` is a compile-only
 configuration used to maximize build coverage and detect regressions.
 
+Documentation:
+--------------
+
+Source code documentation is maintained in a set of man pages, under section 9.
+These pages are located in [`share/man/man9`](../share/man/man9), from the
+top-level of the src tree. Consult [`intro(9)`](https://man.freebsd.org/intro/9)
+for an overview of existing pages.
+
+Some additional high-level documentation of the kernel is maintained in the
+[Architecture Handbook](https://docs.freebsd.org/en/books/arch-handbook/).
+
 Source Roadmap:
 ---------------
 | Directory | Description |