adds 404 page

_404.Rmd

@@ -0,0 +1,16 @@
+<!-- You are nowhere! -->
+
+```{r, echo=FALSE, message=FALSE, fig.asp=1}
+library(tmap)
+library(sf)
+null_island = st_point(c(0, 0))
+null_island = st_sfc(null_island, crs = 4326)
+null_island = st_sf(name = "Null Island", geom = null_island)
+tm_shape(null_island) +
+  tm_graticules(labels.col = "grey40") +
+  tm_text("name", size = 5, fontface = "italic") +
+  tm_layout(bg.color = "lightblue",
+            main.title = "You are here:",
+            main.title.color = "grey40")
+```
+