Extend readme

Author: andreasKroepelin

README.md

@@ -25,3 +25,6 @@ julia> shape_coords("apple-1")
  0.0      0.0      0.0047847  0.0047847  0.014354  0.019139  0.028708  0.043062  …  0.038278  0.028708  0.019139  0.0095694  0.0047847  0.0      0.0      0.0
  0.41627  0.44498  0.47368    0.50239    0.5311    0.55981   0.58852   0.61722      0.23923   0.26794   0.29665   0.32536    0.35407    0.38278  0.41148  0.41627
 ```
+
+Find out what shapes are available by calling `shape_names` or visiting
+[the visual explorer](https://2dshapesstructure.github.io/dataset.html).