docs: update for ipc/cli, tidy a bit

docs/Controlling Ironbar.md

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+Ironbar includes a simple IPC server which can be used to control it programmatically at runtime.
+
+It also includes a command line interface, which can be used for interacting with the IPC server.
+
+# CLI
+
+This is shipped as part of the `ironbar` binary. To view commands, you can use `ironbar --help`. 
+You can also view help per-command, for example using `ironbar set --help`.
+
+Responses are handled by writing their type to stdout, followed by any value starting on the next line.
+Error responses are written to stderr in the same format.
+
+Example:
+
+```shell
+$ ironbar set subject world
+ok
+
+$ ironbar get subject
+ok
+world
+```
+
+# IPC
+
+The server listens on a Unix socket. 
+This can usually be found at `/run/user/$UID/ironbar-ipc.sock`.
+
+Commands and responses are sent as JSON objects, denoted by their `type` key.
+
+The message buffer is currently limited to `1024` bytes. 
+Particularly large messages will be truncated or cause an error.
+
+## Commands
+
+### `ping`
+
+Sends a ping request to the IPC.
+
+Responds with `ok`.
+
+```json
+{
+  "type": "ping"
+}
+```
+
+### `inspect`
+
+Opens the GTK inspector window.
+
+Responds with `ok`.
+
+```json
+{
+  "type": "inspect"
+}
+```
+
+### `get`
+
+Gets an [ironvar](ironvars) value.
+
+Responds with `ok_value` if the value exists, otherwise `error`.
+
+```json
+{
+  "type": "get",
+  "key": "foo"
+}
+```
+
+### `set`
+
+Sets an [ironvar](ironvars) value.
+
+Responds with `ok`.
+
+```json
+{
+  "type": "set",
+  "key": "foo",
+  "value": "bar"
+}
+```
+
+### `load_css`
+
+### `get`
+
+Loads an additional CSS stylesheet, with hot-reloading enabled.
+
+Responds with `ok` if the stylesheet exists, otherwise `error`.
+
+```json
+{
+  "type": "load_css",
+  "path": "/path/to/style.css"
+}
+```
+
+## Responses
+
+### `ok`
+
+The operation completed successfully, with no response data.
+
+```json
+{
+  "type": "ok"
+}
+```
+
+### `ok_value`
+
+The operation completed successfully, with response data.
+
+```json
+{
+  "type": "ok_value",
+  "value": "lorem ipsum"
+}
+```
+
+### `error`
+
+The operation failed.
+
+Message is optional.
+
+```json
+{
+  "type": "error",
+  "message": "lorem ipsum"
+}
+```