Auto merge of rust-lang#8307 - pickfire:alias-help, r=alexcrichton

Show alias in help message

Improve feature discovery of help message
Inspired by x.py help rust-lang/rust#71357
Improves rust-lang#6104

src/bin/cargo/cli.rs

@@ -274,14 +274,14 @@ OPTIONS:
 {unified}
 
 Some common cargo commands are (see all commands with --list):
-    build       Compile the current package
-    check       Analyze the current package and report errors, but don't build object files
+    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
     doc         Build this package's and its dependencies' documentation
     new         Create a new cargo package
     init        Create a new cargo package in an existing directory
-    run         Run a binary or example of the local package
-    test        Run the tests
+    run, r      Run a binary or example of the local package
+    test, t     Run the tests
     bench       Run the benchmarks
     update      Update dependencies listed in Cargo.lock
     search      Search registry for crates