Update docs for undef-all changes

Author: yuhan0

doc/modules/ROOT/pages/usage/cider_mode.adoc

@@ -123,7 +123,7 @@ kbd:[C-u C-c C-c]
 
 | `cider-eval-ns-form`
 | kbd:[C-c C-v n]
-| Eval the ns form.
+| Eval the ns form. If invoked with a prefix argument, undefine all vars and aliases in the ns first.
 
 | `cider-repl-set-ns`
 | kbd:[C-c M-n (M-)n]
@@ -151,15 +151,15 @@ kbd:[C-u C-c C-c]
 
 | `cider-load-buffer`
 | kbd:[C-c C-k]
-| Load (eval) the current buffer.
+| Load (eval) the current buffer. If invoked with a prefix argument, undefine all vars and aliases in the ns before loading.
 
 | `cider-load-file`
 | kbd:[C-c C-l]
-| Load (eval) a Clojure file.
+| Load (eval) a Clojure file. If invoked with a prefix argument, undefine all vars and aliases in the ns before loading.
 
 | `cider-load-all-files`
 | kbd:[C-c C-M-l]
-| Load (eval) all Clojure files below a directory.
+| Load (eval) all Clojure files below a directory. If invoked with a prefix argument, undefine all vars and aliases in each file before loading.
 
 | `cider-ns-refresh`
 | kbd:[C-c M-n (M-)r]
@@ -216,6 +216,10 @@ kbd:[C-c C-d C-e]
 | kbd:[C-c C-u]
 | Undefine a symbol. If invoked with a prefix argument it inverts the value of `cider-prompt-for-symbol`.
 
+| `cider-undef-all`
+| kbd:[C-c C-M-u]
+| Undefine all symbols and aliases in the namespace.
+
 | `cider-test-run-test`
 | kbd:[C-c C-t t] +
 kbd:[C-c C-t C-t]