Add CORS header requirement

transcripts/transcripts.md

@@ -2,6 +2,8 @@
 
 This is the initial spec for the podcast transcript format. There are four possible formats detailed below.
 
+* Some transcript implementations are done in-browser. [CORS headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS) are required to make these files available from other websites. [A CORS tester is available here](https://cors-test.codehappy.dev/), to ensure that transcripts are available within browser-based players.
+
 
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