Add golang to setup docs

[tkporter]

Description

This documentation isn't anywhere anymore. Putting it here as this is the general setup doc that's linked from celo-blockchain.

Tested

n/a

Other changes

n/a

Related issues

n/a

Backwards compatibility

n/a

[codecov]

Codecov Report

Merging #1675 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master    #1675    +/-   ##
========================================
  Coverage   74.38%   74.38%            
========================================
  Files         279      279            
  Lines        7566     7566            
  Branches      663      947   +284     
========================================
  Hits         5628     5628            
  Misses       1824     1824            
  Partials      114      114

Flag	Coverage Δ
#mobile	74.38% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d350720...4b2bed1. Read the comment docs.