cli: improve add command help (#9230)

Author: kinuax

src/poetry/console/commands/add.py

@@ -23,7 +23,7 @@
 
 class AddCommand(InstallerCommand, InitCommand):
     name = "add"
-    description = "Adds a new dependency to <comment>pyproject.toml</>."
+    description = "Adds a new dependency to <comment>pyproject.toml</> and installs it."
 
     arguments: ClassVar[list[Argument]] = [
         argument("name", "The packages to add.", multiple=True)