Update README with info on how to build and generate configure

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

README.md

@@ -60,7 +60,16 @@ Common options:
 Build
 -----
 
-Standard autotools procedure.
+Standard autotools procedure, requires `pkg-config` to locate the `libmnl`
+development files.
+
+    ./configure && make all && sudo make install
 
 At the moment, the kernel module has to be built separately, set
 `KDIR` if building against a kernel in a non-standard location.
+
+When building from GIT, the `configure` script first needs to be generated, this
+requires `autoconf` and `automake` to be installed.  A helper script to generate
+configure is available:
+
+    ./autogen.sh