Edit invocation

Author: pierwill

src/overview.md

@@ -105,6 +105,19 @@ we'll talk about that later.
     low-level types and annotations added. (e.g. an ELF object or wasm).
   - The different libraries/binaries are linked together to produce the final
     binary.
+### Invocation
+
+Compilation begins when a user writes a Rust source program in text
+and invokes the `rustc` compiler on it. The work that the compiler needs to
+perform is defined by command-line options. For example, it is possible to
+enable nightly features (`-Z` flags), perform `check`-only builds, or emit
+LLVM-IR rather than executable machine code. The `rustc` executable call may
+be indirect through the use of `cargo`.
+
+Command line argument parsing occurs in the [`rustc_driver`]. This crate
+defines the compile configuration that is requested by the user and passes it
+to the rest of the compilation process as a [`rustc_interface::Config`].
+
 
 [String interning]: https://en.wikipedia.org/wiki/String_interning
 [`rustc_lexer`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lexer/index.html