Add three Si single crystal EBSD patterns to data module, from external kikuchipy-data repo

[hakonanes]

Signed-off-by: Håkon Wiik Ånes hwaanes@gmail.com

Description of the change

• Add three single crystal Si EBSD patterns, acquired from the same sample position but with three different camera distances (reference/in/operating position, out 5 mm, out 10 mm), to the kikuchipy.data module. The patterns are stored in three separate kikuchipy h5ebsd files (should perhaps be stored in the same file...). These will be used in various user guides, first (will make PR later today) for showing the moving-screen PC estimation technique.
• Add section detailing how to add data to the data module in the contributing guide, contributing.rst.

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

Minimal example of the bug fix or new feature

>>> import kikuchipy as kp
>>> s1 = kp.data.silicon_ebsd_moving_screen_in()
>>> s1
<EBSD, title: si_in Scan 1, dimensions: (|480, 480)>
>>> s1.metadata.Acquisition_instrument.SEM.Detector.EBSD.static_background
array([[7, 8, 7, ..., 7, 7, 7],
       [8, 8, 7, ..., 7, 7, 7],
       [7, 7, 7, ..., 7, 7, 7],
       ...,
       [7, 7, 7, ..., 7, 7, 7],
       [7, 7, 7, ..., 7, 7, 7],
       [7, 7, 7, ..., 7, 7, 7]], dtype=uint8)
>>> s2 = kp.data.silicon_ebsd_moving_screen_out5mm()
>>> s2
<EBSD, title: si_out5mm Scan 1, dimensions: (|480, 480)>
>>> s3 = kp.data.silicon_ebsd_moving_screen_out10mm()
>>> s3
<EBSD, title: si_out10mm Scan 1, dimensions: (|480, 480)>

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the
  unreleased section in doc/changelog.rst.