add: [doc] README

Author: gallypette

README.md

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+# Main features
+
+**d4-pyclient** is python implemention of the [D4 encapsulation
+protocol](https://github.com/D4-project/architecture/tree/master/format). 
+
+It is a low-barrier entry for anyone interested into tinkering with the D4
+protocol or embedding a d4 client into another project. It supports both regular
+types and types defined by meta-header.
+
+# Launching
+
+```shell
+./d4-pyclient.py -h
+usage: d4-pyclient.py [-h] -c CONFIG [-cc]
+
+optional arguments:
+  -h, --help            show this help message and exit
+  -c CONFIG, --config CONFIG
+                        config directory
+  -cc, --check_certificate
+                        check server certificate
+```
+
+# Configuration Files
+
+ of the client configuration can be stored in folder containing the following files:
+
+ - key: your Pre-Shared-Key
+ - snaplen: default is 4096
+ - source: stdin or d4server
+ - destination: stdout, [fe80::ffff:ffff:ffff:a6fb]:4443, 127.0.0.1:4443
+ - type: D4 packet type, see [types](https://github.com/D4-project/architecture/tree/master/format)
+ - uuid: generated automatically if empty
+ - version: protocol version
+ - rootCA.crt: optional : CA certificate to check the server certificate
+ - metaheader.json: optional : a json file describing feed's meta-type [types](https://github.com/D4-project/architecture/tree/master/format)