docs: Corrected usage of pipenv sync Update READEME.md

[0xwitty]

I noticed a issue in the documentation regarding the use of the pipenv sync command. The command is typically run without the -m flag, as pipenv is executed directly rather than as a module through python3.

This change updates the relevant section to remove python3 -m before pipenv, ensuring the documentation reflects the correct usage and avoids potential confusion for users.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.64%. Comparing base (5b56156) to head (78c459a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #12707   +/-   ##
=======================================
  Coverage   70.64%   70.64%           
=======================================
  Files         848      848           
  Lines      173693   173693           
  Branches   173693   173693           
=======================================
+ Hits       122707   122713    +6     
+ Misses      45856    45849    -7     
- Partials     5130     5131    +1     

Flag	Coverage Δ
backward-compatibility	0.16% <ø> (ø)
db-migration	0.16% <ø> (ø)
genesis-check	1.36% <ø> (ø)
linux	69.24% <ø> (+<0.01%)	⬆️
linux-nightly	70.25% <ø> (-0.01%)	⬇️
pytests	1.66% <ø> (ø)
sanity-checks	1.47% <ø> (ø)
unittests	70.48% <ø> (+<0.01%)	⬆️
upgradability	0.20% <ø> (ø)

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[wacban]

Sorry but I'm not familiar with the conventions around python / pipenv. Please seek other reviewer if this change is needed for your project.

From my point of view:
There are plenty of other usages of pipenv as a module across this file so this PR breaks this convention. The old command seems to work so I'm not sure if this change is worth it.