docs/trace-agent: clarify download locations (DataDog#2991)

Author: gbbr

docs/trace-agent/README.md

@@ -17,8 +17,8 @@ The Trace Agent isn't part of the macOS Datadog Agent yet and it needs to be run
 on the side.
 
 - Have the [macOS Agent](https://app.datadoghq.com/account/settings#agent/mac) installed.
-- Download the [latest macOS Trace Agent release](https://github.com/DataDog/datadog-agent/releases/latest). For
-older releases (pre-6.9.0) use the [old repository](https://github.com/DataDog/datadog-trace-agent/releases/).
+- Download the latest macOS Trace Agent release from the [archive repository](https://github.com/DataDog/datadog-trace-agent/releases/).
+Once a newer release is out, it will be available on this repository's [releases section](https://github.com/DataDog/datadog-agent/releases).
 - Run the Trace Agent along the main agent:
 
     `./trace-agent-X.Y.Z-darwin-amd64 -config /opt/datadog-agent/etc/datadog.yaml`