man/man3: add cross references to stdbit(3)

Add cross references to relevant stdbit man pages

Approved by:	markj (mentor)
MFC after:	1 month
Differential Revision: https://reviews.freebsd.org/D53661

share/man/man3/bitstring.3

@@ -461,6 +461,7 @@ make_lpr_available()
 .Ed
 .Sh SEE ALSO
 .Xr malloc 3 ,
+.Xr stdbit 3 ,
 .Xr bitset 9
 .Sh HISTORY
 The

share/man/man3/intro.3

@@ -24,7 +24,7 @@
 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
-.Dd November 27, 2024
+.Dd November 10, 2025
 .Dt INTRO 3
 .Os
 .Sh NAME
@@ -72,13 +72,20 @@ see
 .It database routines
 see
 .Xr db 3
-.It bit operators
+.It bit string operators
 see
 .Xr bitstring 3
+.It bit and byte utilities
+see
+.Xr stdbit 3
 .It string operators
 see
 .Xr string 3
+and
+.Xr bstring 3
 .It character tests and character operators
+see
+.Xr ctype 3
 .It storage allocation
 see
 .Xr mpool 3