Add example to calculate the global gravity disturbance

[aguspesce]

Create an example to calculate the global gravity disturbance using Boule, Esaio and pyGMT to plot.

This idea start in fatiando/ensaio#35

Fix #101

[welcome]

💖 Thank you for opening your first pull request in this repository! 💖

A few things to keep in mind:

• Authorship Guidelines: Our rules for giving you credit for your contributions, including authorship on publications and Zenodo archives.
• Code of Conduct: How we expect people to interact in our projects.

⭐ No matter what, we are really grateful that you put in the effort to do this! ⭐

[aguspesce]

@leouieda and @santisoler, Let me know that do you think about this example.

In addition, I have a problem when I try to complete the documentation. It also happens with the CI.
I think that the problem is pygmt... So @leouieda can you help me with this?

[leouieda]

@aguspesce I'll have a look at the text later but for now upgrading PyGMT and making sure it has the right GMT version will help. These two need to be pinned together.

[leouieda]

Looks good @aguspesce! Just a small suggestion on the colormap and a fix on the data height.

A final step would be to add this to the toctree in the index file so it shows up in the menu.

Let me know when you're satisfied so I can merge 🙂

[aguspesce]

@leouieda, the problem to build the documentation persists. This happens to me on my pc and on the CI.

[leouieda]

Ah that's entirely my fault. This would never work because the Boule docs were being built with pip instead of conda... I'll try to get a fix for that in soon (or if you're up for it, be my guest 🙂).

[leouieda]

@aguspesce alright, I pushed some commits that enable the conda-based build of the docs. Everything passes and looks good to me. If you're happy with this, then please let me know and remove the "WIP" from the title and I'll merge this in.

Thanks for doing this!

[aguspesce]

@leouieda thank you for your help, I didn't have time to see how to fix the documentation.
If you like it, merge it!

[leouieda]

I like it 🙂

[santisoler]

Thanks @aguspesce for this PR! Feel free to add youself to the AUTHORS.md file. You can open a new PR for that.