chore: add top-level CONTRIBUTING.md pointing appropriate place

[soltysh]

Description

While looking through pepr I couldn't find the contributing guide, this will allow users to quickly navigate to appropriate place.

Related Issue

NONE

/assign @cmwylie19

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Unit, Journey, E2E Tests, docs, adr added or updated as needed
• Contributor Guide Steps followed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.55%. Comparing base (1da9f97) to head (ec97dbc).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1442   +/-   ##
=======================================
  Coverage   78.55%   78.55%           
=======================================
  Files          36       36           
  Lines        1716     1716           
  Branches      411      411           
=======================================
  Hits         1348     1348           
  Misses        339      339           
  Partials       29       29           

---- 🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests
• JS Bundle Analysis - Avoid shipping oversized bundles

[cmwylie19]

lgtm!