development(7): redirect users from hier(7)

The layout of the source tree is now only described in README.md. Retain
the cross-reference to hier(7) in SEE ALSO; it is still useful to
readers.

Reviewed by:	imp, emaste
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D37136

share/man/man7/development.7

@@ -23,7 +23,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd August 18, 2022
+.Dd November 1, 2022
 .Dt DEVELOPMENT 7
 .Os
 .Sh NAME
@@ -82,8 +82,9 @@ with an incremented major version number.
 Releases are then branched off STABLE and numbered with consecutive minor
 numbers.
 .Pp
-Layout of the source tree is described in
-.Xr hier 7 .
+The layout of the source tree is described in its
+.Pa README.md
+file.
 Build instructions can be found in
 .Xr build 7
 and