shell: default to "." when no query is specified

use the current tree for "garden shell" when nothing
is specified. This makes it easier to start a shell
in the current directory.

doc/src/changelog.md

@@ -50,6 +50,10 @@
   configuring the `garden.interactive-shell` value.
   ([#26](https://github.com/davvid/garden/pull/26))
 
+- `garden shell` can now be run without any arguments. The tree query now defaults to
+  `.` so that the tree in the current directory is used when nothing is specified.
+  ([#26](https://github.com/davvid/garden/pull/26))
+
 
 ## v1.2.1
 

src/cmds/shell.rs

@@ -8,6 +8,7 @@ use crate::{cmd, errors, eval, model, query};
 #[command(author, about, long_about)]
 pub struct ShellOptions {
     /// Query for trees to build an environment
+    #[arg(default_value = ".")]
     query: String,
     /// Tree to chdir into
     tree: Option<String>,