docs: add base dag API interface

Author: daviddias

API/dag/README.md

@@ -0,0 +1,34 @@
+dag API
+=======
+
+#### `dag.put`
+
+> Store an IPLD format node
+
+##### `Go` **WIP**
+
+##### `JavaScript` - ipfs.dag.put(dagNode, formatMulticodec, hashAlg, callback)
+
+`dagNode` - a DAG node that follows one of the supported IPLD formats.
+
+`formatMulticodec` - The IPLD format multicodec.
+
+`hashAlg` - The hash algorithm to be used over the serialized dagNode.
+
+`callback` must follow `function (err) {}` signature, where `err` is an error if the operation was not successful.
+
+If no `callback` is passed, a [promise][] is returned.
+
+#### `dag.get`
+
+> Retrieve an IPLD format node
+
+##### `Go` **WIP**
+
+##### `JavaScript` - ipfs.object.get(cid, callback)
+
+`cid` is a [CID][https://github.com/ipfs/js-cid] instance.
+
+`callback` must follow `function (err, dagNode) {}` signature, where `err` is an error if the operation was not successful and `dagNode` is the IPLD format DAG node retrieved.
+
+If no `callback` is passed, a [promise][] is returned.