readme: Describe building on Windows

README.md

@@ -1,2 +1,27 @@
 # Octonet PVR
 DigitalDevices [Octonet] (http://www.digital-devices.eu/shop/de/netzwerk-tv/) PVR client addon for [Kodi] (http://kodi.tv)
+
+# Building
+
+## Windows
+1. Create a file `project/cmake/addons/addons/kodi.pvr.octonet/kodi.pvr.octonet.txt` containing a
+   single line `kodi.pvr.octonet file://C:\some\path`. The path doesn't matter and doesn't need to
+   actually exist.
+
+2. Use a shell that has environment variables setup by Visual Studio for the native x86 toolchain.
+   Run the following in a new build directory and adjust paths accordingly:
+
+```
+cmake -G "NMake Makefiles" ^
+    -DCMAKE_BUILD_TYPE=Release ^
+    -DADDONS_TO_BUILD="kodi.pvr.octonet" ^
+    -DADDON_SRC_PREFIX="path_to_where_kodi.pvr.octonet_is" ^
+    -DCMAKE_INSTALL_PREFIX="some_subdirectory" ^
+    -DPACKAGE_ZIP=ON ^
+    "path_to_kodi\project\cmake\addons"
+```
+
+Make sure `ADDON_SRC_PREFIX` points to the parent directory of `kodi.pvr.octonet`.
+
+4. Build the addon by running `nmake`. Run `nmake package-addons` to package a zip file of the
+   addon.