Command line help: Add hint about platform overrides (#375)

- Rename PLATFORMS to PLATFORM
- Add hint about specifying platform multiple times

docs/src/usage.txt

@@ -7,21 +7,22 @@ Arguments:
   [COMMAND]...  The command to show (e.g. `tar` or `git log`)
 
 Options:
-  -l, --list                  List all commands in the cache
-  -f, --render <FILE>         Render a specific markdown file
-  -p, --platform <PLATFORMS>  Override the operating system [possible values: linux, macos, sunos,
-                              windows, android, freebsd, netbsd, openbsd]
-  -L, --language <LANGUAGE>   Override the language
-  -u, --update                Update the local cache
-      --no-auto-update        If auto update is configured, disable it for this run
-  -c, --clear-cache           Clear the local cache
-      --pager                 Use a pager to page output
-  -r, --raw                   Display the raw markdown instead of rendering it
-  -q, --quiet                 Suppress informational messages
-      --show-paths            Show file and directory paths used by tealdeer
-      --seed-config           Create a basic config
-      --color <WHEN>          Control whether to use color [possible values: always, auto, never]
-  -v, --version               Print the version
-  -h, --help                  Print help
+  -l, --list                 List all commands in the cache
+  -f, --render <FILE>        Render a specific markdown file
+  -p, --platform <PLATFORM>  Override the operating system, can be specified multiple times in order
+                             of preference [possible values: linux, macos, sunos, windows, android,
+                             freebsd, netbsd, openbsd]
+  -L, --language <LANGUAGE>  Override the language
+  -u, --update               Update the local cache
+      --no-auto-update       If auto update is configured, disable it for this run
+  -c, --clear-cache          Clear the local cache
+      --pager                Use a pager to page output
+  -r, --raw                  Display the raw markdown instead of rendering it
+  -q, --quiet                Suppress informational messages
+      --show-paths           Show file and directory paths used by tealdeer
+      --seed-config          Create a basic config
+      --color <WHEN>         Control whether to use color [possible values: always, auto, never]
+  -v, --version              Print the version
+  -h, --help                 Print help
 
 To view the user documentation, please visit https://dbrgn.github.io/tealdeer/.

src/cli.rs

@@ -41,10 +41,11 @@ pub(crate) struct Cli {
     )]
     pub render: Option<PathBuf>,
 
-    /// Override the operating system
+    /// Override the operating system, can be specified multiple times in order of preference
     #[arg(
         short = 'p',
         long = "platform",
+        value_name = "PLATFORM",
         action = ArgAction::Append,
     )]
     pub platforms: Option<Vec<PlatformType>>,