docs: Added intial documentation for UPM and start of a porting walkthrough

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

docs/building.md

@@ -0,0 +1,31 @@
+Building UPM                         {#building}
+============
+
+UPM uses cmake in order to make compilation relatively painless. Cmake runs
+build out of tree so the recommended way is to clone from git and make a build/
+directory.
+
+UPM will attempt to build all directories inside src/ and they must contain
+individual CMakeLists.txt files.
+
+~~~~~~~~~~~~~{.sh}
+mkdir build
+cd build
+cmake ..
+make
+~~~~~~~~~~~~~
+
+Our cmake configure has a number of options, `cmake -i` will ask you all sorts
+of interesting questions, you can disable swig modules, build documentation
+etc...
+
+Few recommended options:
+Changing install path from /usr/local to /usr
+-DCMAKE_INSTALL_PREFIX:PATH=/usr
+
+Building debug build:
+-DCMAKE_BUILD_TYPE=DEBUG
+
+Using clang instead of gcc:
+ -DCMAKE_C_COMPILER=/usr/bin/clang -DCMAKE_CXX_COMPILER=/usr/bin/clang
+