made tutorial outputs more presentable (#555)

Closes https://github.com/ooni/probe/issues/1831

internal/tutorial/measurex/chapter10/README.md

@@ -115,7 +115,7 @@ The rest of the program is exactly like in chapter09.
 Let us perform a vanilla run first:
 
 ```bash
-go run -race ./internal/tutorial/measurex/chapter10
+go run -race ./internal/tutorial/measurex/chapter10 | jq
 ```
 
 Take a look at the JSON output. Can you spot that

internal/tutorial/measurex/chapter10/main.go

@@ -116,7 +116,7 @@ func main() {
 // Let us perform a vanilla run first:
 //
 // ```bash
-// go run -race ./internal/tutorial/measurex/chapter10
+// go run -race ./internal/tutorial/measurex/chapter10 | jq
 // ```
 //
 // Take a look at the JSON output. Can you spot that