Re-add erroneously removed function

Tweaking line-breaks, and mentioning the tests.

README.md

@@ -72,10 +72,17 @@ $ sudo cp eksd /usr/local/bin/eksd
 Bam, you've made and installed a binary! Cool!
 
 ### Tests
-eksd’s tests can be run using the `test` Makefile target, or simply
+eksd’s tests can be run from a REPL using `ASDF:TEST-SYSTEM`, or from the
-`(asdf:test-system :eksd)` and `(asdf:test-system :eksd-unix)`.
+Makefile target “test”.
 
-`$ make test`
+```
+* (asdf:test-system :eksd)
+* (asdf:test-system :eksd/unix)
+```
+
+```
+`$ make test
+```
 
 
 ## Misc

src/unix.lisp

@@ -283,6 +283,10 @@
 
 ;; list → list
 (defun de-tail (list)
-  "Remove the last element from a list."
+  "Return a list sans its last element."
   (reverse (cdr (reverse list))))
 
+;; list → object
+(defun tail (list)
+  "Return the last element of a list."
+  (car (last list)))