[docs] add installation instructions for contributors

[databyjp]

Add brief installation instructions for contributors

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.49 🎉

Comparison is base (eb3bf16) 95.43% compared to head (cac02b9) 95.92%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #383      +/-   ##
==========================================
+ Coverage   95.43%   95.92%   +0.49%     
==========================================
  Files          64       64              
  Lines        8165     8171       +6     
==========================================
+ Hits         7792     7838      +46     
+ Misses        373      333      -40     

Impacted Files	Coverage Δ
integration/test_batch.py	98.03% <100.00%> (ø)
test/gql/test_get.py	100.00% <100.00%> (ø)
weaviate/gql/get.py	96.95% <100.00%> (ø)

... and 5 files with indirect coverage changes

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