Document required quoting of booleans in php.ini (#5849)

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

@@ -98,6 +98,14 @@ $meter = OpenTelemetry\API\Globals::meterProvider()->getMeter('name', 'version',
 
 SDK autoloading happens as part of the composer autoloader.
 
+### Configuration from php.ini
+
+When providing configuration through `php.ini`, be sure to protect boolean
+values by double-quoting them, eg `"true"`, `"false"` so that PHP doesn't
+convert them to numbers.
+
+`php.ini`:
+
 ### Excluded URLs
 
 You can disable SDK autoloading if the request URL matches a regular expression.
@@ -134,3 +142,13 @@ There are also a number of PHP-specific configurations:
 
 Configurations can be provided as environment variables, or via `php.ini` (or a
 file included by `php.ini`)
+
+{{% alert title="Boolean values in php.ini" %}} Boolean values in `php.ini`
+should be protected by double-quoting them, for example `"true"` or `"false"`,
+so that PHP doesn't convert them to numbers {{% /alert %}}
+
+```ini
+OTEL_PHP_AUTOLOAD_ENABLED="true"
+OTEL_EXPORTER_OTLP_PROTOCOL=grpc
+OTEL_EXPORTER_OTLP_ENDPOINT=http://collector:4317
+```