Create strings concept

concepts/strings/.meta/config.json

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+{
+    "blurb": "ByteArray is a sequence of ASCII characters longer than 31 characters, written using double quotes",
+    "authors": [
+        "misicnenad"
+    ],
+    "contributors": []
+}

concepts/strings/about.md

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+# String

concepts/strings/introduction.md

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+# Introduction
+
+In Cairo, there's no native type for strings. Instead, you can use a single `felt252` to store a short string of up to 31 characters, or a `ByteArray` for strings of arbitrary length. Short strings use single quotes and `ByteArray` uses double quotes. All characters must follow the ASCII standard.

concepts/strings/links.json

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+[
+    {
+        "url": "https://book.cairo-lang.org/ch02-02-data-types.html#string-types",
+        "description": "String types in the Cairo book"
+    },
+    {
+        "url": "https://starknet-by-example.voyager.online/getting-started/basics/bytearrays-strings.html",
+        "description": "Starknet by Example section on Strings and ByteArrays"
+    },
+    {
+        "url": "https://docs.starknet.io/architecture-and-concepts/smart-contracts/serialization-of-cairo-types/#serialization_of_byte_arrays",
+        "description": "Starknet docs explaining how ByteArray is implemented and how it's serialized"
+    }
+]