docs: enable full-text search (#3004)

docs/.vuepress/config.js

@@ -8,7 +8,12 @@ module.exports = {
     lineNumbers: true
   },
   themeConfig: {
-    lastUpdated: "Last Updated",
+    lastUpdated: true,
+    algolia: {
+      apiKey: '59f0e2deb984aa9cdf2b3a5fd24ac501',
+      indexName: 'tendermint',
+      debug: false
+    },
     nav: [{ text: "Back to Tendermint", link: "https://tendermint.com" }],
     sidebar: [
       {