add numpy examples

[codecov[bot]]

Codecov Report

Merging #49 (df73065) into main (8642c3b) will decrease coverage by 0.06%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #49      +/-   ##
==========================================
- Coverage   93.71%   93.65%   -0.07%     
==========================================
  Files          17       17              
  Lines        6300     6300              
==========================================
- Hits         5904     5900       -4     
- Misses        396      400       +4     

Impacted Files	Coverage Δ
pygmtools/dataset.py	90.83% <0.00%> (-0.45%)	:arrow_down:

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[rogerwwww]

Nice work! Merged.