Update README.md

README.md

@@ -6,6 +6,76 @@
 
 gommunityid is a Golang implementation of the [Community ID flow hashing algorithm](https://github.com/corelight/community-id-spec). Its API design was clearly and obviously inspired by the [Python reference implementation](https://github.com/corelight/pycommunityid).
 
+## Usage
+
+```Go
+package main
+
+import (
+	"fmt"
+	"net"
+
+	"github.com/satta/gommunityid"
+)
+
+func main() {
+	// Get instance for version 1, seed 0
+	cid, _ := gommunityid.GetCommunityIDByVersion(1, 0)
+
+	// Obtain flow tuple. This can be done any way you like.
+	ft := gommunityid.MakeFlowTuple(net.IPv4(1, 2, 3, 4), net.IPv4(5, 6, 7, 8), 9, 10, 1)
+
+	// Calculate Base64-encoded value
+	communityid := cid.CalcBase64(ft)
+	fmt.Printf("%s\n", communityid)
+
+	// Calculate hex-encoded value
+	communityid = cid.CalcHex(ft)
+	fmt.Printf("%s\n", communityid)
+
+	// Calculate byte slice
+	communityidByte := cid.Calc(ft)
+	fmt.Printf("%v\n", communityidByte)
+}
+```
+There is also a [convenience function](https://godoc.org/github.com/satta/gommunityid#PcapFlowTupleSource) for parsing pcap files and automated FlowTuple generation for all supported protocols.
+
+## Command line interface
+
+This package builds a simple [command line tool](cmd/gommunityid.go) to calculate IDs for pcaps:
+```
+$ ./gommunityid pcap
+Usage: gommunityid pcap [options] <pcap-file>
+  -seed uint
+    	seed value (default 0)
+  -version uint
+    	Community ID version (default 1)
+$ gommunityid pcap testdata/tcp.pcap
+1071580904.891921 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 128.232.110.120 66.35.250.204 6 34855 80
+1071580905.035577 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 66.35.250.204 128.232.110.120 6 80 34855
+1071580905.035724 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 128.232.110.120 66.35.250.204 6 34855 80
+1071580905.037333 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 128.232.110.120 66.35.250.204 6 34855 80
+1071580905.181581 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 66.35.250.204 128.232.110.120 6 80 34855
+1071580905.184528 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 66.35.250.204 128.232.110.120 6 80 34855
+1071580905.184844 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 128.232.110.120 66.35.250.204 6 34855 80
+1071580905.184698 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 66.35.250.204 128.232.110.120 6 80 34855
+1071580905.184920 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 128.232.110.120 66.35.250.204 6 34855 80
+1071580905.184736 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 66.35.250.204 128.232.110.120 6 80 34855
+1071580905.203025 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 128.232.110.120 66.35.250.204 6 34855 80
+1071580905.346457 | 1:LQU9qZlK+B5F3KDmev6m5PMibrg= | 66.35.250.204 128.232.110.120 6 80 34855
+```
+and explicit tuples:
+```
+$ gommunityid tuple
+Usage: gommunityid tuple [options] <proto> <srcip> <dstip> <srcport> <dstport>
+  -seed uint
+    	seed value (default 0)
+  -version uint
+    	Community ID version (default 1)
+$ gommunityid tuple 6 66.35.250.204 128.232.110.120 80 34855
+1:LQU9qZlK+B5F3KDmev6m5PMibrg=
+```
+
 ## Author/Contact
 
 Sascha Steinbiss