Update readme with https instead of ssh github install commands

[Balandat]

This caused some confusion for users in #984. This PR also renames pip3 -> pip, since we've long been living in a post-py2 world for long enough.

[facebook-github-bot]

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[codecov-commenter]

Codecov Report

Merging #988 (61e6016) into main (3f8882e) will decrease coverage by 0.07%. The diff coverage is n/a.

:exclamation: Current head 61e6016 differs from pull request most recent head fea450a. Consider uploading reports for the commit fea450a to get more accurate results

@@            Coverage Diff             @@
##             main     #988      +/-   ##
==========================================
- Coverage   94.16%   94.09%   -0.08%     
==========================================
  Files         401      401              
  Lines       34712    34244     -468     
==========================================
- Hits        32688    32223     -465     
+ Misses       2024     2021       -3     

Impacted Files	Coverage Δ
ax/metrics/curve.py	29.50% <0.00%> (-3.31%)	:arrow_down:
ax/metrics/tensorboard.py	35.18% <0.00%> (-1.18%)	:arrow_down:
ax/metrics/noisy_function_map.py	82.75% <0.00%> (-1.12%)	:arrow_down:
ax/utils/common/base.py	94.44% <0.00%> (-1.02%)	:arrow_down:
ax/core/map_data.py	94.79% <0.00%> (-0.54%)	:arrow_down:
ax/core/base_trial.py	96.59% <0.00%> (-0.45%)	:arrow_down:
ax/modelbridge/model_spec.py	93.20% <0.00%> (-0.44%)	:arrow_down:
ax/utils/testing/mock.py	85.29% <0.00%> (-0.43%)	:arrow_down:
ax/modelbridge/generation_node.py	96.66% <0.00%> (-0.40%)	:arrow_down:
ax/core/trial.py	97.29% <0.00%> (-0.27%)	:arrow_down:
... and 87 more

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[facebook-github-bot]

@Balandat has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D36864026