Explicitly prohibit --debounce 0

The `tick_rate` at which the debouncer library checks whether any events
should now be dispatched shouldn't be 0.  It cannot either be any
greater than the debounce rate itself.

Ideally, we may want to *disable* debouncing altogether when the user
passes --debounce 0, but that'd require a special case to be made in the
instrumentation, where we'd bypass the debouncer: that's another package
to depend on, and ultimately deemed no worth the hassle.

Ref: #2937
Ref: https://zola.discourse.group/t/watch-debounce-configuration/2666

Author: ccjmne

docs/content/documentation/getting-started/cli-usage.md

@@ -102,8 +102,10 @@ fail to see your change or get an error, try restarting `zola serve`.
 
 By default, the live reload will be debounced by one full second so as to more
 gracefully handle multiple changes to your input files in rapid succession. You
-have control over that debouncing duration with the debounce flag. You may use
-`-d0` to disable it altogether.
+have control over that debouncing duration with the `--debounce <duration_ms>`
+flag.  
+You may use `-d1` to (virtually) disable it altogether: for technical reasons
+(and keeping things simple), a "debounce" of 0 is not supported.
 
 You can also point to a config file other than `config.toml` like so (note that the position of the `config` option is important):
 

src/cli.rs

@@ -102,8 +102,8 @@ pub enum Command {
         #[clap(long)]
         extra_watch_path: Vec<String>,
 
-        /// Debounce time in milliseconds for the file watcher
-        #[clap(short = 'd', long, default_value_t = 1000)]
+        /// Debounce time in milliseconds for the file watcher (at least 1ms)
+        #[clap(short = 'd', long, default_value_t = 1000, value_parser = clap::value_parser!(u64).range(1..))]
         debounce: u64,
     },