Support //boilerplate/clojure

While this is most likely incomplete or even erroneous, I'd like to start
supporting Clojure in this repository.

boilerplate/clojure/README.md

@@ -0,0 +1,33 @@
+# Clojure Boilerplate
+
+This boilerplate uses `lein` to manage the project.
+
+## Files to change
+
+To use this boilerplate, run the following in a shell:
+
+```shell
+$ cp ~/briefcase/boilerplate/clojure path/to/new-project
+```
+
+After running the above command, change the following files to remove the
+placeholder values:
+
+- `README.md`: Change the title; change the description; drop "Files to change";
+  keep "Getting started"
+- `project.clj`: Change title
+- `src/project.clj`: Change `:doc`; drop `main/foo`
+
+## Getting started
+
+From a shell, run:
+
+```shell
+$ lein repl
+```
+
+From Emacs, navigate to a source code buffer and run:
+
+```
+M-x cider-jack-in
+```