sound: write down a README.md file

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>

1 files changed, 14 insertions, 3 deletions

diff --git a/sound/README.md b/sound/README.md
index 90fc84e..7ff7580 100644
--- a/sound/README.md
+++ b/sound/README.md
@@ -1,3 +1,14 @@
-TBD
-Reference nerdynights: https://nerdy-nights.nes.science/#audio_tutorial-0
-square channels sometimes called pulse channels
+These examples showcase how to produce sound on the NES/Famicom. This is a
+complex topic, but here I'm trying to showcase it at a very fundamental
+level. It's basically the same as to follow the guide from
+[NerdyNights](https://nerdy-nights.nes.science/#audio_tutorial-0), which I read
+extensively, mixing with things I learned by browsing the NESDev wiki. All in
+all we have:
+
+- [beep.s](./beep.s): the most basic example. It constantly sends a C# note to
+  the square 1 channel (mind that square channels are also called "pulse"
+  channels).
+- [select.s](./select.s): same as `beep.s` but while also using the square 2,
+  triangle and noise channels. Note that now everything is muted, and you can
+  unmute each channel by pressing A, B, Start or Select.
+- [scale.s](./scale.s): reproduce a scale of notes over and over.