docs(contributing): lead with the Clojure CLI instead of Leiningen

These libraries build with `deps.edn` and the Clojure CLI, but CONTRIBUTING
named Leiningen as the requirement and used `lein test` / `lein check` as the
commands. Point contributors at the Clojure CLI aliases the repo actually uses.

Author: jsavyasachi

CONTRIBUTING.md

@@ -11,20 +11,20 @@ focused feature contributions are all welcome.
 
 ## Development
 
-This is a Clojure library. You need a JDK and
-[Leiningen](https://leiningen.org/). A project that moved to `deps.edn` uses the
-Clojure CLI instead: see the README.
+This is a Clojure library built with `deps.edn` and the
+[Clojure CLI](https://clojure.org/guides/install_clojure); Leiningen is not
+required. You need a JDK and the Clojure CLI. See the README for the full set
+of aliases.
 
 ```bash
-lein test     # run the test suite
-lein check    # AOT-compile; must be free of reflection warnings
+clojure -M:test    # run the test suite (compiled with *warn-on-reflection* on)
 ```
 
 Requirements for a mergeable change:
 
 - **Tests first.** Add or update tests for the behavior you change. For a bug
   fix, include a regression test that fails before your fix and passes after it.
-- **Green build.** `lein test` passes and `lein check` reports **zero**
+- **Green build.** The test suite passes and the build reports **zero**
   reflection warnings.
 - **No scope creep.** Keep each pull request to one logical change.