Chore: fix docs url (#1730)

Author: pieterocp

composer.json

@@ -6,7 +6,7 @@
     "support": {
         "issues": "https://github.com/open-telemetry/opentelemetry-php/issues",
         "source": "https://github.com/open-telemetry/opentelemetry-php",
-        "docs": "https://opentelemetry.io/docs/php",
+        "docs": "https://opentelemetry.io/docs/languages/php",
         "chat": "https://app.slack.com/client/T08PSQ7BQ/C01NFPCV44V"
     },
     "license": "Apache-2.0",