docs: add the name of the argument

it is platform in the cli and platforms in the pyproject so this was a bit confusing

Author: ManonMarchand

src/ci/mod.rs

@@ -179,7 +179,7 @@ pub struct GenerateCI {
     /// Output path
     #[arg(short = 'o', long, value_name = "PATH", default_value = "-")]
     pub output: PathBuf,
-    /// Platform support [deprecated: use [tool.maturin.generate-ci.github] in pyproject.toml]
+    /// Platform support [deprecated: use [tool.maturin.generate-ci.github] and set 'platforms' in pyproject.toml]
     #[arg(
         id = "platform",
         long,

tests/cmd/generate-ci.stdout

@@ -28,7 +28,8 @@ Options:
           [default: -]
 
       --platform <platform>...
-          Platform support [deprecated: use [tool.maturin.generate-ci.github] in pyproject.toml]
+          Platform support [deprecated: use [tool.maturin.generate-ci.github] and set 'platforms' in
+          pyproject.toml]
 
           Possible values:
           - all:        All