Added GN config for includes

So that depending on the library exports the include path.

Change-Id: Ibcfbafebff76aeed79ff96c2af064325c20f212a
diff --git a/BUILD.gn b/BUILD.gn
index d6e7906..62ebb1c 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -25,11 +25,16 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+config("include_config") {
+  include_dirs = [ "." ]
+}
+
 static_library("linenoise") {
   sources = [
     "linenoise.c",
-    "linenoise.h",
   ]
+
+  public_configs = [ ":include_config" ]
 }
 
 executable("linenoise_example") {