Describe the prelude

Author: chriskrycho

text/0000-template-imports.md

@@ -562,7 +562,50 @@ Then a loose-mode component could invoke them like `<NamedOnly::Greet @name="Chr
 
 ### The “prelude”
 
-<!-- TODO: prelude -->
+While all values used in templates must be explicitly in scope, Ember[^glimmer-prelude] will provide some via a “prelude”.[^prelude] These are always in scope and do not need to be imported.
+
+The helpers in the prelude are:
+
+- `action`
+- `array`
+- `component`
+- `concat`
+- `debugger`
+- `each`
+- `each-in`
+- `fn`
+- `get`
+- `has-block`
+- `has-block-params`
+- `hash`
+- `if`
+- `in-element`
+- `let`
+- `log`
+- `mount`
+- `mut`
+- `on`
+- `outlet`
+- `query-params`
+- `unbound`[^unbound-deprecated]
+- `unless`
+- `yield`
+
+The modifiers in the prelude are:
+
+- `on`
+
+The components in the prelude are:
+
+- `LinkTo`
+- `Input`
+- `Textarea`
+
+[^glimmer-prelude]: Glimmer.js may provide its own prelude. While long-term the two should likely align, this RFC simply takes the _status quo_ as a given
+
+[^prelude]: “Prelude” is the conventional name for this functionality in programming language design.
+
+[^unbound-deprecated]: `unbound` is deprecated, but since it will not be removed till Ember 5.0.0, it should appear in the prelude nonetheless.
 
 
 ### Tooling