update readme

README.md

@@ -2,3 +2,55 @@
 
 Sakua is a guix channel that packages things that you may want but guix
 dosen't have.
+
+Please DO NOT report any issues with the sakura channel to Guix. Sakura is
+not affiliated with the Guix project, and is not supported by them. Any requests
+sent to them will be ignored and waste their time. Please submit all requests
+and git patches to `contact@freyacat.org`.
+
+#### channel
+
+To add sakura to your guix channels, use the following specification.
+
+```scheme
+(channel
+  (name 'sakura)
+  (url "https://g.freya.cat/freya/sakura")
+  (branch "main")
+  (commit
+    "8fb2f9c2fa414754c41c1c73665e3e73e12693ab")
+  (introduction
+    (make-channel-introduction
+      "8fb2f9c2fa414754c41c1c73665e3e73e12693ab"
+      (openpgp-fingerprint
+        "3CD3 65F0 373C EB13 853A  F568 9FBC 6FFD 6D2D BF17"))))
+```
+
+#### substitutes
+
+Sakura hosts a substitute server at `substitutes.freya.cat` with the cuirass
+server running at `cuirass.freya.cat`. You can modify your guix-service-type
+with the following specification to enable the sakura substitute server.
+
+```scheme
+(service guix-service-type
+  (guix-configuration
+    (inherit config)
+    (substitute-urls
+      (append (list "https://substitutes.freya.cat")
+              %default-substitute-urls))
+    (authorized-keys
+      (append (list (local-file ".../sakura.pub"))
+              %default-authorized-guix-keys)))))))
+```
+
+... where sakura.pub is a path to a file holding the following signing key.
+
+```scheme
+(public-key
+ (ecc
+  (curve Ed25519)
+  (q #3E9614FD06AF20F9534DA0DE64FB9004878789744F26FFF2FF381E2EED1DEAC9#)
+  )
+ )
+```