Added initial Tutorial chapter.

Author: DariuszDepta

docs/tutorial/_category_.json

@@ -0,0 +1,8 @@
+{
+  "label": "Tutorial",
+  "position": 8,
+  "link": {
+    "type": "doc",
+    "id": "introduction"
+  }
+}

docs/tutorial/introduction.mdx

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+# Tutorial
+
+This module is a collection of guides for creating CosmWasm smart contracts.
+It will lead you step by step, and explain relevant topics from the easiest to the trickier ones.
+
+The point of these tutorials is not only to tell you about smart contract API but also to show you
+how to write contracts in a clean and maintainable way. We will show you patterns that CosmWasm
+creators established and encourage you to use.