Added first xv6 project and background

initial-xv6/README.md

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+
+# Intro To Kernel Hacking
+
+To develop a better sense of how an operating system works, you will also 
+do a few projects *inside* a real OS kernel. The kernel we'll be using is a
+port of the original Unix (version 6), and is runnable on modern x86
+processors. It was developed at MIT and is a small and relatively
+understandable OS and thus an excellent focus for simple projects.
+More information about xv6, including a very useful book which you might want
+to read, is available [here](https://pdos.csail.mit.edu/6.828/2017/xv6.html).
+
+This first project is just a warmup, and thus relatively light on work. The
+goal of the project is simple: to add a system call to xv6. Your system call,
+**getreadcount()**, simply returns how many times that the **read()** system
+call has been called by user processes since the time that the kernel was
+booted. 
+
+## Your System Call
+
+Your new system call should look have the following return codes and
+parameters: 
+
+```c
+int getreadcount(void)
+```
+
+Your system call returns the value of a counter (perhaps called **readcount**
+or something like that) which is incremented every time any process calls the
+**read()** system call. That's it!
+
+## Tips
+
+Watch this [discussion video](https://www.youtube.com/watch?v=vR6z2QGcoo8) --
+it contains a detailed walk-through of all the things you need to know to
+unpack xv6, build it, and modify it to make this project successful.
+
+One good way to start hacking inside a large code base is to find something
+similar to what you want to do and to carefully copy/modify that. Here, you
+should find some other system call, like **getpid()** (or any other simple
+call). Copy it in all the ways you think are needed, and then modify it to do
+what you need.
+
+Most of the time will be spent on understanding the code. There shouldn't
+be a whole lot of code added.
+
+Using gdb (the debugger) may be helpful in understanding code, doing code
+traces, and is helpful for later projects too. Get familiar with this fine
+tool!
+
+
+
+