chore: add sdk docs to nav (#55)

Related to: zksync-sdk/sdk-docs#7

# What 💻 
* Adds SDK docs to top nav

# Why ✋
* So devs can use SDKs

# Evidence 📷
Include screenshots, screen recordings, or `console` output here
demonstrating that your changes work as intended

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<!-- # Notes 📝
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app.vue

@@ -57,6 +57,10 @@ const links = computed(() => {
       to: '/build',
       active: route.path.startsWith('/build'),
     },
+    {
+      label: 'SDK Docs',
+      to: 'https://zksync-sdk-docs-staging.web.app',
+    },
     {
       label: 'ZK Stack',
       to: '/zk-stack',