docs: instrumentation telemetry usage [LANGPLAT-352] (#13647)

This change adds minimal documentation explaining how contributors
should use Instrumentation Telemetry.

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: emmettbutler

docs/contributing.rst

@@ -106,6 +106,23 @@ Keep the following in mind when writing logging code:
 * Log messages should be standalone and actionable. They should not require context from other logs, metrics or trace data.
 * Log data is sensitive and should not contain application secrets or other sensitive data.
 
+Instrumentation Telemetry
+-------------------------
+
+When you implement a new feature in ddtrace, you should usually have the library emit some Instrumentation
+Telemetry about the feature. Instrumentation Telemetry provides data about the operation of the library in
+real production environments and is often used to understand rates of product adoption.
+
+Instrumentation Telemetry conforms to an internal Datadog API. You can find the API specification in the
+private Confluence space. To send Instrumentation Telemetry data to this API from ddtrace, you can use
+the ``ddtrace.internal.telemetry.telemetry_writer`` object that provides a Python interface to the API.
+
+The most common ``telemetry_writer`` call you may use is ``add_count_metric``. This call generates timeseries
+metrics that you can use to, for example, count the number of times a given feature is used. Another useful
+call is ``add_integration``, which generates telemetry data about the integration with a particular module.
+
+Read the docstrings in ``ddtrace/internal/telemetry/writer.py`` for more comprehensive usage information
+about Instrumentation Telemetry.
 
 .. toctree::
     :hidden:

docs/index.rst

@@ -250,12 +250,12 @@ contacting support.
 Instrumentation Telemetry
 -------------------------
 
-Datadog may gather environmental and diagnostic information about instrumentation libraries; this includes information
+dd-trace-py gathers environmental and diagnostic information at runtime. This includes information
 about the host running an application, operating system, programming language and runtime, APM integrations used,
-and application dependencies. Additionally, Datadog may collect information such as diagnostic logs, crash dumps
+and application dependencies. It also gathers information such as diagnostic logs, crash dumps
 with obfuscated stack traces, and various system performance metrics.
 
-To disable set ``DD_INSTRUMENTATION_TELEMETRY_ENABLED=false`` environment variable.
+To disable this collection, set ``DD_INSTRUMENTATION_TELEMETRY_ENABLED=false`` environment variable.
 
 See our official `datadog documentation <https://docs.datadoghq.com/tracing/configure_data_security#telemetry-collection>`_ for more details.
 

docs/spelling_wordlist.txt

@@ -85,6 +85,7 @@ DES
 deserializing
 django
 docstring
+docstrings
 doctest
 dogpile
 dogpile.cache
@@ -294,6 +295,7 @@ TensorBoard
 testagent
 TestCase
 testrunner
+timeseries
 Timeseries
 timestamp
 tokenizer