Add doc/std/README.md "Modules and Dependencies"
diff --git a/doc/std/README.md b/doc/std/README.md
index 52b02df..102e802 100644
--- a/doc/std/README.md
+++ b/doc/std/README.md
@@ -32,3 +32,36 @@
- [Coroutines](/doc/note/coroutines.md).
- [Initialization](/doc/note/initialization.md).
- [Statuses](/doc/note/statuses.md).
+
+
+## Modules and Dependencies
+
+By default, building Wuffs' standard library builds the entire thing (provided
+that you've defined the `WUFFS_IMPLEMENTATION` C macro), implementing a variety
+of codecs and file formats.
+
+Packages can be individually allow-listed, for smaller binaries and faster
+compiles. Opt in by also defining `WUFFS_CONFIG__MODULES` and then also
+`WUFFS_CONFIG__MODULE__ETC` for each `ETC` (and its dependencies, listed below)
+to enable.
+
+- `ADLER32: BASE`
+- `BMP: BASE`
+- `CBOR: BASE`
+- `CRC32: BASE`
+- `DEFLATE: BASE`
+- `GIF: BASE, LZW`
+- `GZIP: BASE, CRC32, DEFLATE`
+- `JSON: BASE`
+- `LZW: BASE`
+- `NIE: BASE`
+- `PNG: BASE, ADLER32, CRC32, DEFLATE, ZLIB`
+- `WBMP: BASE`
+- `ZLIB: BASE, ADLER32, DEFLATE`
+
+For the [auxiliary modules](/doc/note/auxiliary-code.md):
+
+- `AUX_CBOR: AUX_BASE, BASE, CBOR`
+- `AUX_IMAGE: AUX_BASE, BASE` and whichever image-related modules (and their
+ dependencies) you want, e.g. `GIF`, `PNG`, etc.
+- `AUX_JSON: AUX_BASE, BASE, JSON`
