Point the README at the Slack bot and its walkthrough

One line in the Quickstart block next to `serve`, and one sentence after
the command list linking the setup page and the command-by-command
session walkthrough. The byte-compared admission-gate section is
untouched; tests/test_readme.py stays green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: Shashankss1205

README.md

@@ -162,6 +162,7 @@ grapharc run graph.json --check-only   # admission as a linter; executes nothing
 
 grapharc agent "fix the failing test" --workspace ./sandbox   # agent + the seven core tools
 grapharc serve --port 8000       # the HTTP API (needs the `server` extra)
+python -m grapharc.slack         # the same commands from Slack (needs the `slack` extra)
 
 grapharc models                  # what a model spec resolves to
 grapharc trace <path>            # pretty-print a run trace
@@ -173,6 +174,8 @@ grapharc diff <path> <a> <b>     # what changed between two runs
 
 Eleven commands, and every one of them takes `--json` — in JSON mode the failure is the document rather than a line on stderr. Exit codes are part of the interface: `0` did the job, `1` ran and the answer was negative (an agent stopped short, a run id had no events, two runs differed), `2` could not run at all.
 
+The Slack bot puts most of these commands one `/grapharc …` away from a phone, behind an allowlisting gate that keeps the default spend at zero — setup in [docs/cookbook/07-slack.md](docs/cookbook/07-slack.md), and a command-by-command session, refusals included, in [docs/cookbook/08-slack-walkthrough.md](docs/cookbook/08-slack-walkthrough.md).
+
 The `run` stages use scripted models by default, so they cost nothing and produce the same trace every time. Add `--model` to run one against a real backend — that works for stage1 through stage6 and the capstone; stage0 is pure code with no model in it. `grapharc agent` is the exception: it needs a tool-calling backend and says so rather than degrading, because a scripted model has no `bind_tools` to drive a tool loop with.
 
 Building a graph: