add an example for exporting model to VTK

[yangjiandendi]

Description

added an example for exporting GemPy model to VTK model and getting the vertices of model mesh in Example 01.

Relates to <#922>

Checklist

• My code follows the PEP 8 style guidelines.
• My code uses type hinting for function and method arguments and return values.
• My code contains descriptive and helpful docstrings
  which are formatted per the Google Python Style Guidelines.
• I have created tests which entirely cover my code.
• The test code either 1. demonstrates at least one valuable use case (e.g. integration tests)
  or 2. verifies that outputs are as expected for given inputs (e.g. unit tests).
• New and existing tests pass locally with my changes.

[Leguark]

Hi yangjiandi. Thanks for the pull request, this can be a nice example for other people. However, to add it to the documentation it should be converted to a .py file with similar syntax as the other examples. This makes possible to build sphinx documentation. If you convert it into a .py file I can continue the review.

Cheers

[Leguark]

@gempy-project/gempy_devs is anybody willing to do this? Otherwise I will just close the pr

[javoha]

@gempy-project/gempy_devs is anybody willing to do this? Otherwise I will just close the pr

I contacted the original creator and he will take a look.

[yangjiandendi]

@gempy-project/gempy_devs is anybody willing to do this? Otherwise I will just close the pr

I added it as .py file. Can you check if it is now ok to merge?