docs(astro): Add note about env docs (#13648)

## DESCRIBE YOUR PR
Adding small notice about using environment variables in Astro.

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*Make sure you've checked the following before merging your changes:*

- [ ] Checked Vercel preview for correctness, including links
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Author: s1gr1d

docs/platforms/javascript/guides/astro/index.mdx

@@ -99,7 +99,7 @@ import * as Sentry from "@sentry/astro";
 
 Sentry.init({
   dsn: "___PUBLIC_DSN___",
-  
+
   // Adds request headers and IP for users, for more info visit:
   // https://docs.sentry.io/platforms/javascript/guides/astro/configuration/options/#sendDefaultPii
   sendDefaultPii: true,
@@ -141,12 +141,12 @@ import { nodeProfilingIntegration } from '@sentry/profiling-node';
 
 Sentry.init({
   dsn: "___PUBLIC_DSN___",
-  
+
   // Adds request headers and IP for users, for more info visit: for more info visit:
   // https://docs.sentry.io/platforms/javascript/guides/astro/configuration/options/#sendDefaultPii
   sendDefaultPii: true,
   // ___PRODUCT_OPTION_START___ profiling
-  
+
   integrations: [
     // Add our Profiling integration
     nodeProfilingIntegration(),
@@ -167,6 +167,8 @@ Sentry.init({
 });
 ```
 
+If you want to configure your SDK using environment variables, make sure to follow Astro's documentation on [using environment variables](https://docs.astro.build/en/guides/environment-variables/).
+
 ## Add Readable Stack Traces to Errors
 
 To get readable stack traces in your production builds, set the `SENTRY_AUTH_TOKEN` environment variable in your build environment. You can also add the environment variable to a `.env.sentry-build-plugin` file in the root of your project.