Add Binder link and point to nbviewer

Include Binder instructions and a link to the nbviewer rendered version
of this repository since the GitHub rendering of notebooks is bad and
you can't copy/paste.

Author: leouieda

README.md

@@ -1,8 +1,30 @@
-# Fatiando a Terra Tutorials
+# Fatiando a Terra tutorials
 
 Jupyter notebooks with tutorials for using Fatiando a Terra software to solve
 data problems in geoscience.
 
+## Run the tutorials online
+
+The easiest way to run the code in our tutorials is through the 
+excellent [Binder](https://mybinder.org/) service.
+Click on the badge below and Binder will open up a JupyterLab instance on their
+servers with the tutorial code.
+Easy as that!
+
+[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/fatiando/tutorials/HEAD)
+
+> **WARNING:** Binder will not save any changes you make and may shutdown your
+> JupyterLab without warning. This is a good way to explore but if you intend
+> on editing the notebook then we recommend running things on your machine.
+
+## View the notebooks
+
+You can also browse the code and text in the notebooks online (but won't be
+able to run the code).
+To do so, click on any of the `.ipynb` files in this GitHub repository.
+Alternatively, the [nbviewer](https://nbviewer.org/github/fatiando/tutorials/tree/main/) 
+version can be better and more reliable.
+
 ## License
 
 All Python source code is made available under the BSD 3-clause license. You