Update `web-getting-started` example and tutorial

examples/web-getting-started/src/jsMain/kotlin/Main.kt

 import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.setValue
 import androidx.compose.web.css.padding
 import androidx.compose.web.css.px
 import androidx.compose.web.elements.Button
@@ -8,23 +10,22 @@ import androidx.compose.web.elements.Text
 import androidx.compose.web.renderComposable
 
 fun main() {
-    val count = mutableStateOf(0)
+    var count: Int by mutableStateOf(0)
 
     renderComposable(rootElementId = "root") {
         Div(style = { padding(25.px) }) {
             Button(attrs = {
-                onClick { count.value = count.value - 1 }
+                onClick { count -= 1 }
             }) {
                 Text("-")
             }
 
             Span(style = { padding(15.px) }) {
-                Text("${count.value}")
+                Text("$count")
             }
 
-
             Button(attrs = {
-                onClick { count.value = count.value + 1 }
+                onClick { count += 1 }
             }) {
                 Text("+")
             }

tutorials/Web/Getting_Started/README.md

@@ -115,6 +115,13 @@ fun main() {
     }
 }
 ```
+In case you see an error:
+`Type 'MutableState<TypeVariable(T)>' has no method 'getValue(Nothing?, KProperty<*>)'...` or 
+`Type 'MutableState<TypeVariable(T)>' has no method 'setValue(Nothing?, KProperty<*>, Int)'...`, please add the imports:
+```kotlin
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.setValue
+```
 
 ## Running the project