git: df38b410cfed - releng/15.1 - build.7: Explain update-packages repo signing

The branch releng/15.1 has been updated by cperciva:

URL: https://cgit.FreeBSD.org/src/commit/?id=df38b410cfedfc12250cb66fb7fd8b852fb21335

commit df38b410cfedfc12250cb66fb7fd8b852fb21335
Author:     Alexander Ziaee <ziaee@FreeBSD.org>
AuthorDate: 2026-04-28 16:55:11 +0000
Commit:     Colin Percival <cperciva@FreeBSD.org>
CommitDate: 2026-05-07 22:16:35 +0000

    build.7: Explain update-packages repo signing
    
    Approved by:    re (cperciva)
    MFC after:              3 days
    Reported by:            kevans
    Reviewed by:            kevans, ngie
    Differential Revision:  https://reviews.freebsd.org/D56607
    
    (cherry picked from commit ab98fd3234304ea10db3dee70205828d372c443a)
    (cherry picked from commit dd926806a723b99c9184ce44ab68b83c03fdc173)
---
 share/man/man7/build.7 | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/share/man/man7/build.7 b/share/man/man7/build.7
index 6d040b6f8f02..7947f6186b71 100644
--- a/share/man/man7/build.7
+++ b/share/man/man7/build.7
@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd April 22, 2026
+.Dd April 28, 2026
 .Dt BUILD 7
 .Os
 .Sh NAME
@@ -373,10 +373,18 @@ defaults to
 Create or update the
 .Xr freebsd-base 7
 package repository for the base system.
+.Bl -bullet
+.It
 If an old repository is being updated,
 then packages whose contents have not changed since the previous version
 will be copied into the new repository to avoid needless updating of the
 version number.
+.It
+If
+.Va PKG_REPO_SIGNING_KEY
+is defined, the repo will be signed according to
+.Xr pkg-repo 8 .
+.El
 .It Cm xdev-build
 Builds for the
 .Cm xdev
@@ -1152,6 +1160,7 @@ Study the examples above.
 .Xr config 8 ,
 .Xr etcupdate 8 ,
 .Xr nextboot 8 ,
+.Xr pkg-repo 8 ,
 .Xr shutdown 8
 .Sh HISTORY
 The