fix: Clarify -r/--repositories and --skip-hidden-repositories

This adds information to the help text for the `git clean` options
`-r`/`--repositories` and `--skip-hidden-repositories` to make it
clearer what their relationship is, avoid creating the false
impression that repositories are never deleted in the absence of
`-r`/`--repositories`, and note that `--skip-hidden-repositories`
is sometimes needed to preserve not only separate repositories but
the (probably rarer) case of hidden nested worktrees of the current
repository.

Author: EliahKagan

src/plumbing/options/mod.rs

@@ -583,7 +583,7 @@ pub mod clean {
         /// Remove whole directories.
         #[arg(long, short = 'd')]
         pub directories: bool,
-        /// Remove nested repositories.
+        /// Remove nested repositories, even outside ignored directories.
         #[arg(long, short = 'r')]
         pub repositories: bool,
         /// Pathspec patterns are used to match the result of the dirwalk, not the dirwalk itself.
@@ -592,7 +592,10 @@ pub mod clean {
         /// in reasonable, but often unexpected ways.
         #[arg(long, short = 'm')]
         pub pathspec_matches_result: bool,
-        /// Enter ignored directories to skip repositories contained within.
+        /// Enter ignored directories to skip repositories (and worktrees) contained within.
+        ///
+        /// This identifies and avoids deleting any unrelated repositories, or alternate worktrees
+        /// of this repository, that are nested inside ignored directories eligible for removal.
         #[arg(long)]
         pub skip_hidden_repositories: Option<FindRepository>,
         /// What kind of repositories to find inside of untracked directories.