docs: Tweaks to testing-related notes in the CONTRIBUTING guide (open-telemetry#3414)

Closes: open-telemetry#3412

Author: trentm

CONTRIBUTING.md

@@ -12,6 +12,7 @@ We'd love your help!
   - [Tools used](#tools-used)
   - [General guidance](#general-guidance)
   - [CHANGELOG](#changelog)
+  - [Testing](#testing)
   - [Benchmarks](#benchmarks)
 - [Component Ownership](#component-ownership)
   - [Becoming a Component Owner](#becoming-a-component-owner)
@@ -39,9 +40,14 @@ git clone https://github.com/open-telemetry/opentelemetry-js-contrib.git
 cd opentelemetry-js-contrib
 npm ci
 npm run compile
-npm test
+
+npm run test-services:start
+npm run test:with-services-env
+npm run test-services:stop
 ```
 
+See [Testing](#testing) below for more details on testing.
+
 ## Report a bug or requesting feature
 
 Reporting bugs is an important contribution. Please make sure to include:
@@ -151,7 +157,7 @@ npm run test:with-services-env # runs 'npm test' with envvars from test/test-ser
 npm run test-services:stop     # stops services in Docker
 ```
 
-If you only want to test a single package that dfepends on a service (e.g. the `instrumentation-mongodb`) you can `cd` into it and
+If you only want to test a single package that depends on a service (e.g. the `instrumentation-mongodb`) you can `cd` into it and
 use the same scripts for testing. In this case the script will only start the services needed to test the package.
 
 ```sh
@@ -161,6 +167,12 @@ npm run test:with-services-env      # runs 'npm test' with envvars from test/tes
 npm run test-services:stop          # stop MongoDB service in Docker
 ```
 
+**Browser** tests are run via:
+
+```sh
+npm run test:browser
+```
+
 ### Benchmarks
 
 When two or more approaches must be compared, please write a benchmark in the benchmark/index.js module so that we can keep track of the most efficient algorithm.