docs: add context to example

examples/download-progress/README.md

@@ -1,5 +1,8 @@
 # Download Progress
 This example was built based on [this](https://github.com/charmbracelet/bubbles/discussions/127) discussion.
+This example demonstrates how to download a file from a given URL, and show its progress with a [progress Bubble](https://github.com/charmbracelet/bubbles/).
+The status of the download is updated with [`io.TeeReader`](https://pkg.go.dev/io#TeeReader).
+This calls `Write` which is where we send the updated status with `Program#Send()` 
 
 ## How to Run
 `go build .` in this directory on your machine (in examples/download-progress)