[Docs] Document the Scheme module

doc/modules/index.md

@@ -73,7 +73,7 @@ The following programming languages have enhanced support in Prelude:
 - [Ruby](ruby.md)
 - Rust
 - Scala
-- Scheme
+- [Scheme](scheme.md)
 - SCSS
 - Shell
 - TypeScript

doc/modules/scheme.md

@@ -0,0 +1,28 @@
+# Prelude Scheme
+
+!!! Note
+
+    This module builds on top of the shared [Lisp Base](lisp.md) module.
+
+## lisp-mode
+
+Not much to say here, as `scheme-mode` is configured to use Prelude's
+default Lisp settings.
+
+## Geiser
+
+This module bundles [Geiser](https://www.nongnu.org/geiser/), a popular interactive
+programming environment for Scheme. People familiar with Common Lisp's SLIME will
+feel right at home with Geiser.
+
+Note that Geiser supports many Scheme implementations:
+
+* Guile 2.2 or better
+* Chicken 4.8.0 or better
+* MIT/GNU Scheme 9.1 or better
+* Chibi Scheme 0.7 or better
+* Chez Scheme 9.4 or better
+* Gambit 4.9 or better
+* Racket 6.0 or better
+
+You can fire Geiser with `M-x geiser`.