More README

cmd/linktool/README.md

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+# linktool
+Command-line tool to encode and decode link URLs, useful during testing.
+
+```
+./linktool -h
+./linktool [encode|decode] encode and decode link URLs
+
+encode
+  -action string
+        [open|initial_open|click] (default "open")
+  -message_id string
+        message_id (default "0000123456789abcdef0")
+  -rcpt_to string
+        rcpt_to (default "any@example.com")
+  -target_link_url string
+        URL of your target link (default "https://example.com")
+  -tracking_url string
+        URL of your tracking service endpoint (default "http://localhost:8888")
+
+decode url
+```
+
+Example: encode a URL
+```
+ ./linktool encode -tracking_url http://localhost:8888 -rcpt_to fred@thetucks.com -action click -target_link_url https://thetucks.com -message_id 00000deadbeeff00d1337
+
+http://localhost:8888/eJxUzLEOQiEMRuF3-WciGAaTTr4JwbaIUSKBMhnf_Ybxnv18P2Q2EBgOltb4gFDN-iTvraotfs8Lfxsc2nyml4AQdqJZHqqlhCDXGG9wGNw3VYbK_fT-jwAAAP__f2Mg1g==
+```
+
+Decode a URL
+```
+./linktool decode http://localhost:8888/eJxUzLEOQiEMRuF3-WciGAaTTr4JwbaIUSKBMhnf_Ybxnv18P2Q2EBgOltb4gFDN-iTvraotfs8Lfxsc2nyml4AQdqJZHqqlhCDXGG9wGNw3VYbK_fT-jwAAAP__f2Mg1g==
+
+JSON: {"act":"c","t_url":"https://thetucks.com","msg_id":"00000deadbeeff00d1337","rcpt":"fred@thetucks.com"}
+Equivalent to encode -tracking_url http://localhost:8888 -rcpt_to fred@thetucks.com -action click -target_link_url https://thetucks.com -message_id 00000deadbeeff00d1337
+```