Add buy btc using Moonpay general instructions and an Android example (#51)

* Update android examples

* Add buy btc moonpay doc for android and more general instructions

* Update src/guide/buy_btc.md

Co-authored-by: Ruben <36157890+ubbabeck@users.noreply.github.com>

* Update src/guide/buy_btc.md

Co-authored-by: Ruben <36157890+ubbabeck@users.noreply.github.com>

---------

Co-authored-by: Ruben <36157890+ubbabeck@users.noreply.github.com>

src/guide/buy_btc.md

@@ -2,6 +2,10 @@
 
 This section of the Breez SDK documentation provides an example on purchasing Bitcoin using Moonpay as the provider. The example code snippet demonstrates how to initiate a Bitcoin purchase transaction using the Breez SDK.
 
+The SDK will generate a Bitcoin address and prepare a URL using the specified provider. The user needs to open the URL and proceed with the provider flow to buy the Bitcoin.
+
+Once the buy is completed, the provider will transfer the Bitcoin to the generated address and Breez SDK will add the received Bitcoin to the Lightning balance.
+
 <custom-tabs category="lang">
 
 <div slot="title">Rust</div>
@@ -32,8 +36,17 @@ do {
 <div slot="title">Android</div>
 <section>
 
-```kotlin,ignore
-// TODO add docs
+```kotlin
+try {
+    // Choose your provider
+    val provider = BuyBitcoinProvider.MOONPAY
+    // request the url to proceed with the Bitcoin acquisition
+    val url = sdk.buyBitcoin(BuyBitcoinRequest(provider)).url
+    // Opens the url in the browser to buy on provider's site
+    startActivity(Intent(Intent.ACTION_VIEW, Uri.parse(url)))
+} catch (e: Exception) {
+    // Handle error
+}
 ```
 </section>
 

src/guide/install.md

@@ -56,7 +56,7 @@ dependencies {
 }
 ```
 
-See [the example](https://github.com/breez/breez-sdk/tree/main/libs/sdk-bindings/bindings-android/example) for more details
+See [the example](https://github.com/breez/breez-sdk-examples/tree/main/Android) for more details
 
 ## React Native
 

src/guide/payments.md

@@ -44,7 +44,10 @@ do {
 
 ```kotlin,ignore
 try {
-    val invoice = sdk.receivePayment(3000L.toULong(), "Invoice for 3000 sats")
+    val invoice = sdk.receivePayment(ReceivePaymentRequest(
+        3000L.toULong(),
+        "Invoice for 3000 sats",
+    ))
 } catch (e: Exception) {
     // handle error
 }

src/guide/receive_onchain.md

@@ -39,7 +39,7 @@ do {
 
 ```kotlin,ignore
 try {
-    val swapInfo = sdk.receiveOnchain()
+    val swapInfo = sdk.receiveOnchain(ReceiveOnchainRequest())
     // Send your funds to the bellow bitcoin address
     val address = swapInfo.bitcoinAddress
 } catch (e: Exception) {