Update README to explain how to add the channel

README.md

@@ -5,8 +5,10 @@ used in project [GÉODE](https://geode-project.github.io/).
 
 ## How to use
 
-It hopes to eventually become a proper guix channel but has been only used so
-far with the `-L` option in commands like `build`, `shell` or `system`.
+The packages contained in this repository can be used in two ways with `guix`:
+you can simply load the guile definitions it contains dynamically as you need
+them, or you can add it to your known channels and have them appear as any
+official `guix` package.
 
 ### Quick try
 
@@ -20,7 +22,29 @@ should work and return results.
 
 ### Add the channel
 
-[TODO](https://guix.gnu.org/fr/manual/devel/en/html_node/Creating-a-Channel.html#Creating-a-Channel)
+To use this channel and get access to the packages it defines, add the following
+block to your channels configuration file at `~/.config/guix/channels.scm`.
+
+```guile
+(channel
+ (name 'geode)
+ (url "https://gitlab.liris.cnrs.fr/geode/geode-packages")
+ (branch "main"))
+```
+
+This file is meant to describe a list of channels, so the block above will
+usually join other similar blocks as arguments to the `(cons* …)` function,
+modifying the `%default-channels` value that is used when the file is missing.
+Thus, if `geode` is the first channel you add to your `guix`, the whole file you
+will create should look like:
+
+```guile
+(cons* (channel
+         (name 'geode)
+         (url "https://gitlab.liris.cnrs.fr/geode/geode-packages")
+         (branch "main"))
+       %default-channels)
+```
 
 ## Disclaimer