Add a section to the docsite about node administration, cover attachment upload/download.

docs/source/index.rst

@@ -28,6 +28,7 @@ Read on to learn:
    data-model
    messaging
    running-the-trading-demo
+   node-administration
 
 .. toctree::
    :maxdepth: 2

docs/source/node-administration.rst

@@ -0,0 +1,41 @@
+Node administration
+===================
+
+When a node is running, it exposes an embedded web server that lets you monitor it, upload and download attachments,
+access a REST API and so on.
+
+Uploading and downloading attachments
+-------------------------------------
+
+Attachments are files that add context to and influence the behaviour of transactions. They are always identified by
+hash and they are public, in that they propagate through the network to wherever they are needed.
+
+All attachments are zip files. Thus to upload a file to the ledger you must first wrap it into a zip (or jar) file. Then
+you can upload it by running this command from a UNIX terminal:
+
+.. sourcecode:: shell
+
+   curl -F myfile=@path/to/my/file.zip http://localhost:31338/attachments/upload
+
+The attachment will be identified by the SHA-256 hash of the contents, which you can get by doing:
+
+.. sourcecode:: shell
+
+   shasum -a 256 file.zip
+
+on a Mac or by using ``sha256sum`` on Linux. Alternatively, check the node logs. There is presently no way to manage
+attachments from a GUI.
+
+An attachment may be downloaded by fetching:
+
+.. sourcecode:: shell
+
+   http://localhost:31338/attachments/DECD098666B9657314870E192CED0C3519C2C9D395507A238338F8D003929DE9
+
+where DECD... is of course replaced with the hash identifier of your own attachment. Because attachments are always
+containers, you can also fetch a specific file within the attachment by appending its path, like this:
+
+.. sourcecode:: shell
+
+   http://localhost:31338/attachments/DECD098666B9657314870E192CED0C3519C2C9D395507A238338F8D003929DE9/path/within/zip.txt
+