cidr: add page (#15176)

Signed-off-by: Bruno Schaatsbergen <git@bschaatsbergen.com>

pages/common/cidr.md

@@ -0,0 +1,24 @@
+# cidr
+
+> Simplifies IPv4/IPv6 CIDR network prefix management with counting, overlap checking, explanation, and subdivision.
+> More information: <https://github.com/bschaatsbergen/cidr>.
+
+- Explain a CIDR range:
+
+`cidr explain {{10.0.0.0/16}}`
+
+- Check whether an address belongs to a CIDR range:
+
+`cidr contains {{10.0.0.0/16}} {{10.0.14.5}}`
+
+- Get a count of all addresses in a CIDR range:
+
+`cidr count {{10.0.0.0/16}}`
+
+- Check whether two CIDR ranges overlap:
+
+`cidr overlaps {{10.0.0.0/16}} {{10.0.14.0/22}}`
+
+- Divide a CIDR range into a specific number of networks:
+
+`cidr divide {{10.0.0.0/16}} {{9}}`