docs: document need for rustfmt, have ./check look for it

Sponsored-by: author

1 files changed, 15 insertions, 5 deletions

diff --git a/README.md b/README.md
index 2550850..f55d584 100644
--- a/README.md
+++ b/README.md
@@ -27,15 +27,25 @@ See <https://subplot.liw.fi/> for the home page.
 ## Hacking Subplot
 
 Subplot is written using the Rust programming language, so the usual
-workflow for Rust applies. To build run `cargo build`, to run tests in
-Rust run `cargo test`. You probably need to install Rust using rustup:
-the version packaged in a Linux distribution is likely too old.
+workflow for Rust applies.
+
+* To build: `cargo build`
+* To run tests: `cargo test`
+* To format code: `cargo fmt`
+
+You probably need to install Rust using rustup: the version packaged
+in a Linux distribution is likely too old. When you install Rust,
+ensure you have the following installed:
+
+* `rustc`
+* `cargo`
+* `rustfmt`
 
 To run the whole test suite, including testing all examples and
 Subplot self tests, run `./check` at the root of the source tree.
 
-You'll need to install build dependencies installed. On a system
-running Debian or a derivative of it:
+You'll need to install some build dependencies. On a system running
+Debian or a derivative of it:
 
 ~~~sh
 $ sudo apt-get install build-essential git debhelper dh-cargo python3 \