Improve and clarify matrix raw command's help

- Use proper rst syntax for stating commands/cli/monospaced (double
  backticks), which improves rendered docs and still looks good enough
  in --help on the shell.
- Clarify which config settings we are referring to.
- Format token precedence list with \b (displays linebreaks as-is;
  renders nicely on the shell as well as in the Sphinx docs.
- Add an "insecure warning"

synadm/cli/matrix.py

@@ -95,16 +95,24 @@ def raw_request_cmd(helper, endpoint, method, data, data_file, token, prompt):
     """ Execute a raw request to the Matrix API.
 
     The endpoint argument is the part of the URL _after_ the configured base
-    URL and Matrix path (see `synadm config`). A simple get request would e.g
-    look like this: `synadm matrix raw client/versions`
+    URL (actually "Synapse base URL") and "Matrix API path" (see ``synadm
+    config``). A get request could look like this: ``synadm matrix raw
+    client/versions`` URL encoding must be handled at this point. Consider
+    enabling debug outputs via synadm's global flag ``-vv``
 
-    Use either --token or --prompt to provide a user's token and execute Matrix
-    commands on their behalf. Respect the privacy of others! Be responsible!
+    Use either ``--token`` or ``--prompt`` to provide a user's token and
+    execute Matrix commands on their behalf. Respect the privacy of others!
+    Act responsible!
 
+    \b
     The precedence rules for token reading are:
-    1. Interactive input using --prompt; 2. Set on CLI via --token string;
-    3. Read from environment variable $MTOKEN; 4. Preconfigured admin token
-    set in synadm's config file.
+    1. Interactive input using ``--prompt``;
+    2. Set on CLI via ``--token``
+    3. Read from environment variable ``$MTOKEN``;
+    4. Preconfigured admin token set via ``synadm config``.
+
+    Caution: Passing secrets as CLI arguments or via environment variables is
+    not considered secure. Know what you are doing!
     """
     if prompt:
         token = click.prompt("Matrix token", type=str)