Add opentelemetry to the Readme.md

Author: iokiwi

Readme.md

@@ -77,6 +77,7 @@ functions:
 | Newrelic         | `${bref-extra:newrelic-php-81}`        |
 | ODBC Snowflake   | `${bref-extra:odbc-snowflake-php-81}`  |
 | OpenSwoole       | `${bref-extra:openswoole-php-81}`      |
+| OpenTelemetry    | `${bref-extra:opentelemetry-php-81}`   |
 | Oracle           | `${bref-extra:oci8-php-80}`            |
 | Pcov             | `${bref-extra:pcov-php-81}`            |
 | PostgreSQL       | `${bref-extra:pgsql-php-81}`           |