Doc: add README_jclklib.md

This document will provide basic architecture and simplified code flow
for connect/subscribe/notification messages.

This is a live document.

Signed-off-by: Noor Azura Ahmad Tarmizi <[email protected]>

jclklib/README_jclklib.md

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+# JCLKLIB codeflow
+
+Jclklib is a 2-part implementation for C/C++ application to obtain
+ptp4l events via pub/sub method using a library api call.
+
+It provides a library jcklib.so (aka client-runtime library) and a daemon
+jclib_proxy.
+
+In short we have :
+           FRONT-END              MIDDLE-PIPE               BACK-END
+c/c++ app <---------> jclklib.so <----------> jclklib_proxy<--------> ptp4l
+        (library call)           (using msq)      |         (via UDS)
+                                                  |
+                                              libptpmgmt.so
+
+* **c++ app** - Customer application that will be linking to jclklib.so library. Header file and sample test cpp file will be provided.
+
+* **jcklib.so** - A dynamic library that provides a set of APIs to customer application : connect/disconnect, subscribe to ptp4l daemon. This library is written in C++. It will have a permissive licence. It communicates with jclkib_proxy using message queues.
+
+* **jclklib_proxy** - A daemon that is using libptpmgmt api to establish connection and subscribe towards ptp4l events. The communication is establish using ptp4l UDS (/var/run/ptp4l as we now assumed it is always installed in the same local machine as the ptp4l)
+
+## Connect message flow (simplified code walkthrough)
+