Improve urllib3 instrumentation examples

[andremm]

Description

There's one instrumentation example inside urllib3 that doesn't run. This PR fixes the example, so it runs. It also ports instrumentation examples to README.rst to match the examples in the urllib3 documentation.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

1. Clone contrib repo: git clone https://github.com/open-telemetry/opentelemetry-python-contrib
2. Clone OTel Python repo: git clone https://github.com/open-telemetry/opentelemetry-python
3. Access the contrib repo: cd opentelemetry-python-contrib
4. Create a virtual env: python3 -m venv otelvenv
5. Activate the virtual env: source otelvenv/bin/activate
6. Install common dependencies:

pip install opentelemetry-distro/ opentelemetry-instrumentation/ \
 ../opentelemetry-python/opentelemetry-semantic-conventions/ \
 ../opentelemetry-python/opentelemetry-api/ \
 ../opentelemetry-python/opentelemetry-sdk/ \
 ../opentelemetry-python/opentelemetry-proto/ \
 ../opentelemetry-python/exporter/opentelemetry-exporter-otlp-proto-common

7. Install urllib3 specific requirements:

pip install -r instrumentation/opentelemetry-instrumentation-urllib3/test-requirements.txt

8. Copy the instrumentation examples inside the instrumentation main __init__.py file into different Python files and try to run them.

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[xrmx]

If you go multiline with arguments, formatters format every line with a trailing comma

[xrmx]

Suggested change

	response_hook=response_hook
	response_hook=response_hook,

[xrmx]

Suggested change

	response_hook=response_hook
	response_hook=response_hook,