examples: add math example (#1461)

* examples: add math example

* docs: add math example

docs/examples/math/App.vue

@@ -0,0 +1,31 @@
+<script setup>
+import { ref } from 'vue'
+import { VueFlow } from '@vue-flow/core'
+import { Background } from '@vue-flow/background'
+import { initialEdges, initialNodes } from './initial-elements.js'
+import ValueNode from './ValueNode.vue'
+import OperatorNode from './OperatorNode.vue'
+import ResultNode from './ResultNode.vue'
+
+const nodes = ref(initialNodes)
+
+const edges = ref(initialEdges)
+</script>
+
+<template>
+  <VueFlow class="math-flow" :nodes="nodes" :edges="edges" fit-view-on-init>
+    <template #node-value="props">
+      <ValueNode :id="props.id" :data="props.data" />
+    </template>
+
+    <template #node-operator="props">
+      <OperatorNode :id="props.id" :data="props.data" />
+    </template>
+
+    <template #node-result="props">
+      <ResultNode :id="props.id" />
+    </template>
+
+    <Background />
+  </VueFlow>
+</template>