add csharp snippets

snippets/csharp/StaticChannelBackup.cs

@@ -0,0 +1,19 @@
+using Breez.Sdk;
+
+public class StaticChannelBackupSnippets
+{
+    public void StaticChannelBackup(BlockingBreezServices sdk)
+    {
+        // ANCHOR: static-channel-backup
+        try
+        {
+            var backupData = BreezSdkMethods.StaticBackup(
+                new StaticBackupRequest("<working directory>"));
+        }
+        catch (Exception)
+        {
+            // Handle error
+        }
+        // ANCHOR_END: static-channel-backup
+    }
+}