Document missing server config options (#18122)

I was looking into the `USE_FROZEN_DICTS` option during the review of
https://github.com/element-hq/synapse/pull/18103#discussion_r1935876168
and noticed that there are several other server config options that
aren't in the docs.

2 files changed, 59 insertions, 0 deletions

diff --git a/changelog.d/18122.doc b/changelog.d/18122.doc
new file mode 100644

index 0000000000..b7bb7107e2
--- /dev/null
+++ b/changelog.d/18122.doc
@@ -0,0 +1 @@
+Document missing server config options (`daemonize`, `print_pidfile`, `user_agent_suffix`, `use_frozen_dicts`, `manhole`).
diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md

index a5f23149ec..fdca48caf0 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -162,6 +162,53 @@ Example configuration:
 pid_file: DATADIR/homeserver.pid
 ```
 ---
+### `daemonize`
+
+Specifies whether Synapse should be started as a daemon process. If Synapse is being
+managed by [systemd](../../systemd-with-workers/), this option must be omitted or set to
+`false`.
+
+This can also be set by the `--daemonize` (`-D`) argument when starting Synapse.
+
+See `worker_daemonize` for more information on daemonizing workers.
+
+Example configuration:
+```yaml
+daemonize: true
+```
+---
+### `print_pidfile`
+
+Print the path to the pidfile just before daemonizing. Defaults to false.
+
+This can also be set by the `--print-pidfile` argument when starting Synapse.
+
+Example configuration:
+```yaml
+print_pidfile: true
+```
+---
+### `user_agent_suffix`
+
+A suffix that is appended to the Synapse user-agent (ex. `Synapse/v1.123.0`). Defaults
+to None
+
+Example configuration:
+```yaml
+user_agent_suffix: " (I'm a teapot; Linux x86_64)"
+```
+---
+### `use_frozen_dicts`
+
+Determines whether we should freeze the internal dict object in `FrozenEvent`. Freezing
+prevents bugs where we accidentally share e.g. signature dicts. However, freezing a
+dict is expensive. Defaults to false.
+
+Example configuration:
+```yaml
+use_frozen_dicts: true
+```
+---
 ### `web_client_location`
 
 The absolute URL to the web client which `/` will redirect to. Defaults to none.
@@ -596,6 +643,17 @@ listeners:
 ```
 
 ---
+### `manhole`
+
+Turn on the Twisted telnet manhole service on the given port. Defaults to none.
+
+This can also be set by the `--manhole` argument when starting Synapse.
+
+Example configuration:
+```yaml
+manhole: 1234
+```
+---
 ### `manhole_settings`
 
 Connection settings for the manhole. You can find more information