chore: Update CONTRIBUTING instructions for running tests using Appra…

…isal (#1167)

* chore: Update contributing instructions for running tests

* Update CONTRIBUTING.md

Co-authored-by: Kayla Reopelle <87386821+kaylareopelle@users.noreply.github.com>

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Co-authored-by: Kayla Reopelle <87386821+kaylareopelle@users.noreply.github.com>

CONTRIBUTING.md

@@ -80,6 +80,12 @@ For example, to test `opentelemetry-instrumentation-action_pack` you would:
  2. Install the bundle with `bundle install`
  3. Run the tests with `bundle exec rake`
 
+Note: Some test suites make use of [Appraisal](https://github.com/thoughtbot/appraisal), a library for testing against different versions of dependencies. To run tests in suites that use Appraisal:
+
+ 1. Change directory to the instrumentation you'd like to test, ex: `instrumentation/action_pack`
+ 2. Install the bundle with `bundle exec appraisal install`
+ 3. Run the tests with `bundle exec appraisal rake test`
+
 ### Docker setup
 
 We use Docker Compose to configure and build services used in development and