Update stage 11 instructions

Author: vic-ma

course-definition.yml

@@ -794,39 +794,41 @@ stages:
     name: "Gzip compression"
     difficulty: medium
     description_md: |
-      In this stage, you'll add support for returning responses compressed using gzip.
+      In this stage, you'll add support for [`gzip` compression](https://www.gzip.org/) to your HTTP server.
 
       ### Tests
 
       The tester will execute your program like this:
-
-      ```bash
-      ./your_server.sh
+      ```
+      $ ./your_server.sh
       ```
 
-      It'll then send an HTTP `GET` request to the `/echo/<a-random-string>` endpoint. In the request, it'll include an Accept-Encoding header like: `Accept-Encoding: gzip`.
-      As an example, here's a request you might receive:
-
+      Then, the tester will send a `GET` request to the `/echo/{str}` endpoint on your server. The request will contain an `Accept-Encoding` header that includes `gzip`.
       ```
-      GET /echo/foo HTTP/1.1
-      Host: localhost:4221
-      User-Agent: curl/7.64.1
-      Accept-Encoding: gzip
+      $ curl -v -H "Accept-Encoding: gzip" http://localhost:4221/echo/abc | hexdump -C
       ```
 
-      Your server must respond with a `200 OK` response. The response should have a `Content-Encoding: gzip` header present. The response body should be the random string sent in the request, gzip encoded. And the `Content-Length` header should be the length of the gzip encoded data.
-      Here's the response you're expected to send back:
-      If the raw string was `foo`, the hex encoded data would be `gzip-encoded-data`
-      Hex representation of it would be `1f8b08008c643b6602ff4bcbcf07002165738c03000000`
+      Your server's response must contain the following:
+      - `200` response code.
+      - `Content-Type` header set to `text/plain`.
+      - `Content-Encoding` header set to `gzip`.
+      - `Content-Length` header set to the size of the compressed body.
+      - Response body set to the `gzip`-compressed `str` parameter.
 
       ```
       HTTP/1.1 200 OK
       Content-Encoding: gzip
       Content-Type: text/plain
       Content-Length: 23
 
-      gzip-encoded-data
+      1F 8B 08 00 00 00 00 00  // Hexadecimal representation of the response body
+      00 03 4B 4C 4A 06 00 C2
+      41 24 35 03 00 00 00
       ```
 
+      ### Notes
+
+      - To check that your compressed body is correct, you can run `echo -n <uncompressed-str> | gzip | hexdump -C`.
+      - It's normal for a very short string like `abc` to increase in size when compressed.
     marketing_md: |
       In this stage, you'll add support for encoding the response body using `gzip`.