[Docs] Document cider-macroexpansion-display-namespaces

This came up in #3080.

Author: bbatsov

doc/modules/ROOT/pages/debugging/macroexpansion.adoc

@@ -23,3 +23,18 @@ expansion buffer (which is internally using
 kbd:[u]
 | Undo the last in-place expansion performed in the macroexpansion buffer.
 |===
+
+== Configuration
+
+The option `cider-macroexpansion-display-namespaces` controls whether to display
+namespaces in the macroexpansion buffer. It can be set to one of the following:
+
+* `qualified` - Vars are fully-qualified in the expansion.
+* `none`- Vars are displayed without namespace qualification.
+* `tidy`(default) - Vars that are :refer-ed or defined in the current namespace
+  are displayed with their simple name, non-referred vars from other namespaces
+  are referred using the alias for that namespace (if defined), other vars are
+  displayed fully qualified.
+
+The option `cider-macroexpansion-print-metadata` controls whether to print the var metadata
+in the macroexpansion buffer. It's set to `nil` by default.