format images, add license and demo links

README.md

@@ -1,8 +1,10 @@
+        ([click here to online demonstration](https://ppkrauss.github.io/Sfc4q/) for Desktop Firefox or Chrome)
+
 # Sfc4q classes
 
 *Space-filling curves*  (SFCs) can be used to index discrete grids, including the [Geospatial ones](http://docs.opengeospatial.org/as/15-104r5/15-104r5.html). Each cell in the grid is associated with an index, which can be produced by an SFC.  In this project, we are particularly interested in hierarchical grids with a recurring ​partition of quadrilateral cells in 4 regions​:
 
-![](docs/assets/quadrilateral-refinementRatio4.png)
+<img align="right" src="docs/assets/quadrilateral-refinementRatio4.png">
 
 Therefore, we are interested in any SFC that is valid for indexing hierarchical grid of refinement-ratio-4 quadrilateral cells, abbreviated **SFC-4q**, or *Sfc4q* as adopted in the project's name and classes names.
 
@@ -12,23 +14,23 @@ In this project we are also interested in [geocodes](https://en.wikipedia.org/wi
 
 The framework can be used as simple standard interface for a set of SFC algorithms, like Hilbert, Morton or other.
 
-![](docs/assets/umlClass01-intro.png)
+<img align="right" src="docs/assets/umlClass01-intro.png">
 
 The algorithms themselves are "concrete classes". But the standardization of basic methods, such as *endode()* and *decode()*, is not the issue, there are a lot of generic and reusable methods, so the best way is to extend a generic class with these reusable methods, and implement the concrete algorithm  as specialization. This project is a set of abstract and concrete classes.
 
-Other important issue for SFC-4q is the generalization for "half levels" described in [this PDF article](http://osm.codes/_foundations/art3.pdf). It is also independent of the concrete algorithms. The illustration bellou is hou these classes uas implemented:
+Other important issue for SFC-4q is the generalization for "half levels" described in [this PDF article](https://zenodo.org/record/2536584). It is also independent of the concrete algorithms. The illustration bellou is hou these classes uas implemented:
 
 ![](docs/assets/umlClass02-Sfc4q.png)
 
 * [**GSfc4q**](https://ppkrauss.github.io/Sfc4q/docs/jsDocs/GSfc4q.html): the "Generalized Sfc4q" class.
 
-* [**GSfc4qLbl**](https://ppkrauss.github.io/Sfc4q/docs/jsDocs/GSfc4qLbl.html): a generaliation of GSfc4q,  to translate *key*, *bkey* and cell identifiers (cell IDs) into human-readable labels (lbl). To preserve hierarchy, this translation uses the concept of [Sized Natural number](http://osm.codes/_foundations/art1.pdf), implemented in Javascript by the class SizedBigInt.
+* [**GSfc4qLbl**](https://ppkrauss.github.io/Sfc4q/docs/jsDocs/GSfc4qLbl.html): a generaliation of GSfc4q,  to translate *key*, *bkey* and cell identifiers (cell IDs) into human-readable labels (lbl). To preserve hierarchy, this translation uses the concept of [Natural Codes](http://osm.codes/_foundations/art1.pdf), implemented in Javascript by the class SizedBigInt.
 
 * **GSfc4qLbl_Hilbert**: the "concrete class" that implements the [Hilbert curve](https://en.wikipedia.org/wiki/Hilbert_curve).
 
 * **GSfc4qLbl_Morton**:the "concrete class" that implements the [Morton curve](https://en.wikipedia.org/wiki/Z-order_curve) (also  Z-order curve).
 
-* [**SizedBigInt**](https://ppkrauss.github.io/Sfc4q/docs/jsDocs/SizedBigInt.html): it is a complementar tool for use BigInt (mainly 64 bits unsigned integers) as hierarchical indexes and obtain its string representations.
+* [**SizedBigInt**](https://ppkrauss.github.io/Sfc4q/docs/jsDocs/SizedBigInt.html): it is a complementar tool for use BigInt (mainly 64 bits unsigned integers) as hierarchical indexes and obtain its string representations, and an implementation of the Natural Codes.
 
 See [classes documentation](https://ppkrauss.github.io/Sfc4q/docs/jsDocs).
 
@@ -37,3 +39,10 @@ See [classes documentation](https://ppkrauss.github.io/Sfc4q/docs/jsDocs).
 * [**GridOfCurve**](https://ppkrauss.github.io/Sfc4q/docs/jsDocs/GridOfCurve.html)
 
 * [**GridOfCurve_D3**](https://ppkrauss.github.io/Sfc4q/docs/jsDocs/GridOfCurve_D3.html)
+
+## LICENSE
+
+Content, data and algorithms: **CC0 1.0**,  Public Domain Dedication.
+
+[![License: CC0](https://upload.wikimedia.org/wikipedia/commons/thumb/6/69/CC0_button.svg/88px-CC0_button.svg.png)](http://creativecommons.org/publicdomain/zero/1.0)
+