httpflow: add page (#4493)

pages/common/httpflow.md

@@ -0,0 +1,24 @@
+# httpflow
+
+> A command line utility to capture and dump HTTP streams.
+> More information: <https://github.com/six-ddc/httpflow>.
+
+- Capture traffic on all interfaces:
+
+`httpflow -i {{any}}`
+
+- Use a bpf-style capture to filter the results:
+
+`httpflow {{host httpbin.org or host baidu.com}}`
+
+- Use a regexp to filter requests by urls:
+
+`httpflow -u '{{regex}}'`
+
+- Read packets from pcap format binary file:
+
+`httpflow -r {{out.cap}}`
+
+- Write the output to a directory:
+
+`httpflow -w {{path/to/directory}}`