Added example wirekit README

wirekits/example/README.md

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+# Example Wire Kit
+The wire kit implemented in ``main.cpp`` hooks into all entries to ``open`` and ``openat`` system calls and logs the filenames given to them. In ``wirekit_command_exit``, it prints the compiled list of all opened files. An important note is the reason to **not print** in the system call entry hooks themselves: the hosted commands use the same shell as the wire kit, by default. If you run e.g. ``vim`` but have a wire kit print in the middle of it, the output messes with ``vim``'s own control of the console. To prevent this, either accumulate all output until the command has finished executing or spawn a separate shell from within the wire kit, either when it is prepared or a command is started.