Add NFT metadata standard and reference scheme info (#90)

Dapp-development/Guides/NFT-metadata-standard.md

@@ -0,0 +1,60 @@
+## NFT Metadata Standard
+
+NFTs on CENNZnet should be linked to an offchain metadata file in the JSON format with the following minimal structure:
+
+```json
+{
+    "name": "A name for this token",
+    "description": "A description for this token",
+    "image": "The default image for this token",
+    "encodingFormat": "image/png",
+    "attributes": [
+        { "trait_type": "background", "value": "blue" },
+        { "trait_type": "power_level", "value": 9001 },
+    ],
+    "animation_url": "https://example.com/animation-1.html",
+}
+```
+
+| Field  | Description|
+| ------ | -------|
+| `name` | display name for the token |
+|`description` | human friendly description of the token |
+|`image` | default display image for the token |
+|`encodingFormat` (optional) | denotes the encoding format of `image` according to the common [IANA media types](https://www.iana.org/assignments/media-types/media-types.xhtml). If omitted `image/png` is assumed |
+|`attributes` | arbitrary length array of key/value objects where `trait_type` is the key and `value` is value. Can be left empty |
+|`animation_url` | URL to a multi-media attachment for the token e.g. GLTF, GLB, WEBM, MP4, M4V, OGV, and OGG or audio-only extensions MP3, WAV, and OGA. `animation_url` also supports HTML pages, allowing you to build rich experiences and interactive NFTs using JavaScript canvas, WebGL, and more.|
+| `*` | any additional fields are allowed e.g. for application specific purposes |
+
+## Metadata Reference Scheme
+
+When creating an NFT series a metadata reference scheme must be specified.
+There are two supported schemes with different tradeoffs.
+
+### 1) HTTP(S)
+
+An HTTP API provides a JSON document given a valid serial number from the series.
+`https://<host>/<path>+/<serialNumber>` e.g. https://api.example.com/tokens/123
+This is the most common and flexible scheme allowing developers to alter and host token metadata.
+
+### 2) IPFS directory
+
+The entire series metadata should be known beforehand and uploaded as an IPFS directory.
+The metadata files in the directory should be named according to their serial numbers.
+This option is less common, provides a commitment to token immutability preventing developers from changing metadata as it is stored by the IPFS protocol.
+
+```dir
+metadata
+├── 0.json
+├── 1.json
+├── 2.json
+└── 3.json
+```
+
+e.g. `ipfs://bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi/123.json` returns the metadata JSON document for token with serial number 123
+
+### 3) Unique IPFS / Arweave files
+
+This will require the series creator to upload individual CIDs/file hashes with each token.
+It provides the same as 2) with flexibility to extend a collection or create metadata incrementally.
+This option is not supported initially for simplicity sake.

_Sidebar.md

@@ -15,6 +15,7 @@
 	- [Network Fees](Dapp-development/Guides/Network-fees)
 	- [Token Economy](Dapp-development/Guides/Token-Economy)
 	- [NFT Design](Dapp-development/Guides/How-to-design-NFTs)
+	- [NFT Metadata Standard](Dapp-development/Guides/NFT-metadata-standard)
 	- [NFT Royalties](Dapp-development/Guides/NFT-royalties)
 	- [Smart Contracts](Dapp-development/Guides/Using-Smart-Contracts-on-CENNZnet)