Repair stg branch --describe

Running `stg branch --describe` with no arguments would result in a panic.
The description argument was meant to be marked as required, which it now
is.

Author: jpgrayson

src/cmd/branch.rs

@@ -204,7 +204,11 @@ fn make() -> clap::Command<'static> {
                 .override_usage("stg branch {--describe,-d} <description> [branch]")
                 .alias("--description")
                 .about("Set the branch description")
-                .arg(Arg::new("description").help("Description string for branch"))
+                .arg(
+                    Arg::new("description")
+                        .help("Description string for branch")
+                        .required(true),
+                )
                 .arg(
                     Arg::new("branch-any")
                         .help("Branch to describe")

t/t1008-branch-description.sh

@@ -4,6 +4,12 @@ test_description='Test branch descriptions'
 
 . ./test-lib.sh
 
+test_expect_success \
+    'Missing description argument' '
+    general_error stg branch --describe 2>err &&
+    grep -e "required arguments were not provided" err
+'
+
 test_expect_success \
     'Description of non-stgit branch' '
     test "$(stg branch)" = "master" &&