fix(help): Provide better commands heading for styling

In working on rust-lang#12578, I felt it would be weird to style the entire
statement about commands but it also felt weird to not style it.  So
this change explores and alternatively way of communicating the
information.

src/bin/cargo/cli.rs

@@ -542,7 +542,7 @@ Usage: {usage}
 Options:
 {options}
 
-Some common cargo commands are (see all commands with --list):
+Commands:
     build, b    Compile the current package
     check, c    Analyze the current package and report errors, but don't build object files
     clean       Remove the target directory
@@ -559,6 +559,7 @@ Some common cargo commands are (see all commands with --list):
     publish     Package and upload this package to the registry
     install     Install a Rust binary. Default location is $HOME/.cargo/bin
     uninstall   Uninstall a Rust binary
+    ...         See all commands with --list
 
 See 'cargo help <command>' for more information on a specific command.\n",
         )

tests/testsuite/cargo/help/stdout.log

@@ -18,7 +18,7 @@ Options:
   -Z <FLAG>                 Unstable (nightly-only) flags to Cargo, see 'cargo -Z help' for details
   -h, --help                Print help
 
-Some common cargo commands are (see all commands with --list):
+Commands:
     build, b    Compile the current package
     check, c    Analyze the current package and report errors, but don't build object files
     clean       Remove the target directory
@@ -35,5 +35,6 @@ Some common cargo commands are (see all commands with --list):
     publish     Package and upload this package to the registry
     install     Install a Rust binary. Default location is $HOME/.cargo/bin
     uninstall   Uninstall a Rust binary
+    ...         See all commands with --list
 
 See 'cargo help <command>' for more information on a specific command.