Create README.md

Author: raspi

README.md

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+# ip-range-to-CIDR
+
+Convert IP address range to CIDR.
+
+## Examples
+
+    % ip-range-to-cidr 192.168.0.0 192.168.0.255
+    192.168.0.0/24
+
+Figuring out github.com's AS range:
+
+    % systemd-resolve github.com                                                                                          
+    github.com: 140.82.118.3                       -- link: phy0
+
+    -- Information acquired via protocol DNS in 45.6ms.
+    -- Data is authenticated: no
+
+     % openrdap-client --json --type ip 140.82.118.3 | jq -r '"\(.startAddress) \(.endAddress)"' | xargs ./ip-range-to-cidr
+     140.82.112.0/20