_content: change generic min example to index

This avoids importing the constraints package, which is no longer in
the standard library.

For golang/go#50792

Change-Id: I0e0f48d414e87418a1fe95e500bb7629127007cc
Reviewed-on: https://go-review.googlesource.com/c/website/+/383254
Reviewed-by: Eli Bendersky‎ <[email protected]>
Reviewed-by: Eli Bendersky <[email protected]>
Trust: DO NOT USE <[email protected]>
Run-TryBot: DO NOT USE <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

_content/doc/play/index-dev.txt

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+)
+
+// The index function returns the index of the first occurrence of v in s,
+// or -1 if not present.
+func index[E comparable](s []E, v E) int {
+	for i, vs := range s {
+		if v == vs {
+			return i
+		}
+	}
+	return -1
+}
+
+func main() {
+	s := []int{1, 3, 5, 2, 4}
+	fmt.Println(index(s, 3))
+	fmt.Println(index(s, 6))
+}

_content/play.tmpl

@@ -36,7 +36,7 @@
     <option value="multi.txt">Multiple Files</option>
     <option value="sleep.go">Sleep</option>
     <option value="test.go">Test Function</option>
-    <option value="min-dev.txt">Generic min</option>
+    <option value="index-dev.txt">Generic index</option>
     </select>
     </div>
   </div>