doc: another generics example (#6031)

doc/docs.md

@@ -1651,6 +1651,32 @@ user := users_repo.find_by_id(1)?
 post := posts_repo.find_by_id(1)?
 ```
 
+Another example:
+```v
+fn compare<T>(a, b T) int {
+    if a < b {
+        return -1
+    }
+    if a > b {
+        return 1
+    }
+    return 0
+}
+
+println(compare<int>(1,0)) // Outputs: 1
+println(compare<int>(1,1)) //          0
+println(compare<int>(1,2)) //         -1
+
+println(compare<string>('1','0')) // Outputs: 1
+println(compare<string>('1','1')) //          0
+println(compare<string>('1','2')) //         -1
+
+println(compare<float>(1.1, 1.0)) // Outputs: 1 
+println(compare<float>(1.1, 1.1)) //          0
+println(compare<float>(1.1, 1.2)) //         -1
+```
+
+
 ## Concurrency
 
 V's model of concurrency is very similar to Go's. To run `foo()` concurrently, just