Update readme with build information.

README.md

-Note: If this is being used in the vanilla kernel, the following should be added to the end of the thread task struct in sched.h:
+
+Overview
+--------
+
+This is the AC/Threaded C (THC) code from the Barrelfish team, with
+bug fixes and extensions for our own asynchronous ipc (using libfipc).
+
+While the original Barrelfish code has support for other platforms
+and other architectures, the current build system for libasync just
+supports the Linux kernel on x86_64. (The build, etc. can be extended
+if and when it's needed.)
+
+Kernel Patch
+------------
+
+Note: If this is being used in the vanilla kernel, the following should 
+be added to the end of the struct task_struct definition in 
+include/linux/sched.h:
+
 #ifdef CONFIG_LAZY_THC
          struct ptstate_t *ptstate;
 #endif
+
+and you should add an initializer to include/linux/init_task.h. Finally,
+you should re-build your kernel with CONFIG_LAZY_THC set.
+
+Build Instructions
+------------------
+
+Assume your libasync repository is at absolute path ABS_PATH.
+
+First, build libfipc. Make sure the git submodule has been pulled in; do:
+
+      cd ABS_PATH
+      git submodule update --init
+
+Then, configure and build it:
+
+      mkdir fipc-build
+      mkdir fipc-install
+      cd fast-ipc-module
+      ./autogen.sh
+      cd ../fipc-build
+      ../fast-ipc-module/configure --with-kernel-headers=<path to kernel> \
+              --prefix=ABS_PATH/fipc-install
+      make
+      make install
+
+Next, configure and build libasync:
+
+      cd ..
+      mkdir async-build
+      mkdir async-install
+      ./autogen.sh
+      cd async-build
+      ../configure --with-kernel-headers=<path to kernel> \
+              --prefix=ABS_PATH/async-install \
+              --with-libfipc=ABS_PATH/fipc-install \
+              --enable-kernel-tests-build
+      make
+      make install
+
+This will install libasync.a in async-install/lib and the headers in
+async-install/include. It will also put kernel module tests in the lib/
+folder. Note that these tests depend on libfipc, and are statically linked
+with it. So, you don't need to do any further linking after they are
+built; they are ready to go.