Display help message when pipx install is run without arguments (#1266

)

* Display help message when `pipx install` is run without arguments

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

changelog.d/1266.bugfix.md

@@ -0,0 +1 @@
+Display help message when `pipx install` is run without arguments.

src/pipx/main.py

@@ -378,7 +378,7 @@ def _add_install(subparsers: argparse._SubParsersAction, shared_parser: argparse
         description=INSTALL_DESCRIPTION,
         parents=[shared_parser],
     )
-    p.add_argument("package_spec", help="package name(s) or pip installation spec(s)", nargs="*")
+    p.add_argument("package_spec", help="package name(s) or pip installation spec(s)", nargs="+")
     add_include_dependencies(p)
     p.add_argument(
         "--force",