opam: edit synopsis and add instructions

Author: yasunariw

README.md

@@ -4,15 +4,16 @@ A Slackbot for GitHub monorepos. Configure how repo notifications should be rout
 
 ## Setting Up
 
-Install dependencies via OPAM.
+Install via OPAM:
 
-```sh
-opam install --deps-only .
+```
+opam install monorobot
 ```
 
-Then, build with Dune.
+Or install dependencies and build locally:
 
 ```sh
+opam install --deps-only .
 make
 ```
 

monorobot.opam

@@ -1,7 +1,7 @@
 opam-version: "2.0"
 name: "monorobot"
 version: "0.1"
-synopsis: "Notification bot"
+synopsis: "Notification bot for monorepos"
 description: "Notification bot to handle webhook events and post notifications to Slack."
 maintainer: "Ahrefs <[email protected]>"
 authors: "Ahrefs <[email protected]>"