protcol/exporter: Clarify that the env vars do not need to be impleme…

…nted directly in the exporter

specification/protocol/exporter.md

@@ -10,7 +10,9 @@ This document specifies the configuration options available to the OpenTelemetry
 
 ## Configuration Options
 
-The following configuration options MUST be available to configure the OTLP exporter. Each configuration option MUST be overridable by a signal specific option.
+The following configuration options MUST be available to configure the OTLP exporter.
+The configuration options MAY be implemented directly in the OTLP exporter, in the SDK, or in a seperate component (e.g. environment-based autoconfiguration component).
+Each configuration option MUST be overridable by a signal specific option.
 
 - **Endpoint (OTLP/HTTP)**: Target URL to which the exporter is going to send spans or metrics. The endpoint MUST be a valid URL with scheme (http or https) and host, MAY contain a port, SHOULD contain a path and MUST NOT contain other parts (such as query string or fragment). A scheme of https indicates a secure connection. When using `OTEL_EXPORTER_OTLP_ENDPOINT`, exporters MUST construct per-signal URLs as  [described below](#endpoint-urls-for-otlphttp). The per-signal endpoint configuration options take precedence and can be used to override this behavior (the URL is used as-is for them, without any modifications). See the [OTLP Specification][otlphttp-req] for more details.
   - Default:  `http://localhost:4318` [1]