Differentiate between Wallet SDK and JS SDK (#229)

* Differentiate between Wallet SDK and JS SDK

There's been some confusion on what tutorial to use for what. Hoping that renaming the sections will help users correctly decide what to use.

Change titles for Wallet SDK and payment application sections

Added sentence in the Overview that recommends the Wallet SDK

* Update overview.mdx

docs/building-apps/example-application-tutorial/_category_.json

@@ -1,6 +1,6 @@
 {
   "position": 55,
-  "label": "Example Application Tutorial",
+  "label": "Build a Payment App with the JS SDK",
   "link": {
     "type": "generated-index"
   }

docs/building-apps/overview.mdx

@@ -7,6 +7,8 @@ Stellar is an open-source distributed ledger that you can use as a backend to po
 
 Stellar has built-in logic for key storage, creating accounts, signing transactions, tracking balances, and queries to the Stellar database, and anyone can use the network to issue, store, transfer, and trade assets.
 
+This documentation will walk you through how to build a wallet with the Wallet SDK (recommended) or an example payment application with the JS Stellar SDK (legacy).
+
 ## Anchors
 
 Many Stellar assets connect to real-world currencies, and Stellar has open protocols for integrating deposits and withdrawals of these assets via the [anchor network](https://stellar.org/learn/anchor-basics). Because of this, a Stellar-based application can take advantage of real banking rails and connect to real money.

docs/building-apps/wallet/_category_.json

@@ -1,6 +1,6 @@
 {
   "position": 45,
-  "label": "Build a Wallet",
+  "label": "Build a Wallet with the Wallet SDK",
   "link": {
     "type": "generated-index"
   }