Clarify the behavior of the attributes field on registerOTel function

.changeset/strange-papayas-battle.md

@@ -0,0 +1,5 @@
+---
+"@vercel/otel": patch
+---
+
+Update documentation

packages/otel/README.md

@@ -47,7 +47,7 @@ Registers the OpenTelemetry SDK with the specified service name and the default
 Registers the OpenTelemetry SDK with the specified configuration. Configuration options include:
 
 - `serviceName`: The name of your service, used as the app name in many OpenTelemetry backends.
-- `attributes`: The resource attributes. By default, `@vercel/otel` configures relevant Vercel attributes based on [the environment](https://vercel.com/docs/projects/environment-variables/system-environment-variables), such as `vercel.env`, `vercel.runtime`, `vercel.host`, etc.
+- `attributes`: The resource attributes. By default, `@vercel/otel` configures relevant Vercel attributes based on [the environment](https://vercel.com/docs/projects/environment-variables/system-environment-variables), such as `vercel.env`, `vercel.runtime`, `vercel.host`, etc. The specified attributes are merged with default Vercel environment attributes.
 - `instrumentations`: A set of instrumentations. By default, `@vercel/otel` configures "fetch" instrumentation.
 - `instrumentationConfig`: Customize configuration for predefined instrumentations:
   - `fetch`: Customize configuration of the predefined "fetch" instrumentation:

packages/otel/src/types.ts

@@ -56,7 +56,7 @@ export interface Configuration {
   serviceName?: string;
 
   /**
-   * The resource attributes.
+   * The additional resource attributes to apply to all spans.
    * By default, `@vercel/otel` configures relevant Vercel attributes based on the
    * [environment](https://vercel.com/docs/projects/environment-variables/system-environment-variables),
    * including:
@@ -68,6 +68,8 @@ export interface Configuration {
    * - `vercel.sha` - the Vercel deployment Git SHA (`VERCEL_GIT_COMMIT_SHA` environment variable).
    * - `vercel.host` - the Vercel deployment host for the Git SHA (`VERCEL_URL` environment variable).
    * - `vercel.branch_host` - the Vercel deployment host for the branch (`VERCEL_BRANCH_URL` environment variable).
+   * 
+   * Any additional attributes will be merged with the default attributes.
    */
   attributes?: ResourceAttributes;