Add missing using instrumentation libraries pages: PHP (#4370)

Co-authored-by: Phillip Carter <[email protected]>

content/en/docs/languages/php/libraries.md

@@ -0,0 +1,55 @@
+---
+title: Using instrumentation libraries
+linkTitle: Libraries
+weight: 40
+cSpell:ignore: Packagist
+---
+
+{{% docs/languages/libraries-intro "PHP" %}}
+
+## Use instrumentation libraries
+
+If a library doesn't include OpenTelemetry support, you can use
+[instrumentation libraries](/docs/specs/otel/glossary/#instrumentation-library)
+to generate telemetry data for a library or framework.
+
+The OpenTelemetry PHP extension includes instrumentation libraries for many
+common PHP frameworks. For example,
+[the Laravel instrumentation](https://github.com/open-telemetry/opentelemetry-php-contrib/tree/main/src/Instrumentation/Laravel)
+automatically creates [spans](/docs/concepts/signals/traces/#spans) based on the
+application activity.
+
+## Setup
+
+Each instrumentation library is a Composer package. To install it, run the
+following command:
+
+```sh
+php composer.phar install {name-of-instrumentation}:{version-number}
+```
+
+Where `{name-of-instrumentation}` is the Packagist reference for the specific
+instrumentation you want to use.
+
+You can turn off any instrumentation by adding its identifier to the
+`OTEL_PHP_DISABLED_INSTRUMENTATIONS` environment variable.
+
+## Available instrumentation libraries
+
+For a list of available instrumentations, see
+[OpenTelemetry instrumentation packages](https://packagist.org/search/?query=open-telemetry&tags=instrumentation)
+on Packagist.
+
+## Next steps
+
+After you've set up instrumentation libraries, you might want to add
+[additional instrumentation](/docs/languages/php/instrumentation) to collect
+custom telemetry data.
+
+You might also want to configure an appropriate exporter to
+[export your telemetry data](/docs/languages/php/exporters) to one or more
+telemetry backends.
+
+You can also check the
+[automatic instrumentation for PHP](/docs/languages/php/automatic) for existing
+library instrumentations.