Trim after-install to the first-run path

Editing behaviour, the plugin tools and the search prerequisite all live in
README.md in more detail; repeating them here made the one document a user
actually reads at install time as long as the reference. What stays is what
changes what they do next.

after-install.md

@@ -88,20 +88,6 @@ can live in either file. Environment variables take precedence over
    (answers every message). The `/join` reply prints both lines ready to
    paste, with the room ID filled in.
 
-   Editing works as a correction: fix a typo in your sent message within
-   5 minutes and Hermes restarts his answer with the corrected text. If he had
-   ignored the message because an `@mention` was missing, editing the mention
-   in makes him answer after all.
-
-   The bot can also talk first: ask it to post a summary into a channel it
-   answers in, or to DM someone who has already written to it. Those are the
-   `chatto_send_room` / `chatto_send_dm` tools, which obey the same room rules
-   as inbound messages — a channel listed in neither mention room list stays
-   read-only. A third tool, `chatto_list_rooms`, turns a channel name into the
-   room ID those tools want. `hermes tools` lists all of them.
-
-   Reading needs no setup of its own: `chatto_get_history` and
-   `chatto_get_message` open what a room or thread already says.
-   `chatto_search_messages` additionally needs message search switched on for
-   the Chatto server itself — if it is off, that one tool says so and every
-   other tool keeps working.
+   That is the first-run path done. Everything beyond answering a message —
+   corrections by editing, the plugin tools, and server-side prerequisites such
+   as message search — is in `README.md`.