Document the dashboard, the artifacts command and what moved with them

Covers this round of CLI work: the serve dashboard and its keys, the refusal
to start a second engine for one installation, --plain, --gpus and the
declared-not-detected card count, `fluksio artifacts`, the age column,
`fluksio.logger` inside a node, the server extra, per-directory study module
names, and an export whose columns no longer move with the selection.

docs/code/nodes.md

@@ -110,6 +110,18 @@ Because the address is the content's hash, a sweep whose fifty configs share
 one preprocessed input stores it once, and a reference stays valid wherever the
 store is reachable from — including on another machine.
 
+`fluksio artifacts RUN NAME` is how one comes back out at a terminal.
+
+### `fluksio.logger`
+
+A node's `print` is kept as that node's logs, and so is anything on
+`fluksio.logger` — the same logger the SDK exports at top level, so code that
+runs both inside a node and outside one says it the same way:
+
+```python
+fluksio.logger.info("resuming from epoch %d", start)
+```
+
 ### Media
 
 Say what the bytes are and the port can be typed for them: