chore: update CONTRIBUTING.md

[mayurkale22]

Which problem is this PR solving?

• Update CONTRIBUTING.md with how to run benchmarks.

[codecov-io]

Codecov Report

Merging #445 into master will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #445      +/-   ##
==========================================
+ Coverage   95.32%   95.41%   +0.08%     
==========================================
  Files         124      124              
  Lines        6166     6171       +5     
  Branches      505      510       +5     
==========================================
+ Hits         5878     5888      +10     
+ Misses        288      283       -5

Impacted Files	Coverage Δ
.../opentelemetry-plugin-dns/test/utils/assertSpan.ts	100% <0%> (ø)	⬆️
...try-plugin-dns/test/functionals/dns-enable.test.ts	100% <0%> (ø)	⬆️
...in-dns/test/integrations/dnspromise-lookup.test.ts	90.82% <0%> (+0.91%)	⬆️
packages/opentelemetry-plugin-dns/src/utils.ts	70% <0%> (+1%)	⬆️
...ry-plugin-dns/test/integrations/dns-lookup.test.ts	94.16% <0%> (+1.66%)	⬆️
...kages/opentelemetry-plugin-dns/test/utils/utils.ts	57.14% <0%> (+23.8%)	⬆️