Configure cache in Makefile

Makefile

@@ -17,9 +17,11 @@ ifneq ($(CORES),)
 endif
 
 nix_args := $(keep_going_args) $(jobs_args) $(cores_args)
-nix_build := nix-build $(nix_args)
-nix_shell := nix-shell $(nix_args)
-run_in_nix_shell := $(nix_shell) --run
+
+append_to_nix_config := NIX_CONFIG="$$(printf "%s\n" "$$NIX_CONFIG" && cat hacking/binary-cache/fragment.nix.conf)"
+
+nix_build := $(append_to_nix_config) nix-build $(nix_args)
+nix_shell := $(append_to_nix_config) nix-shell $(nix_args)
 
 ifeq ($(IN_NIX_SHELL_FOR_MAKEFILE),)
 	# TODO

README.md

@@ -121,7 +121,10 @@ the crates which use them:
 
 ### Quick start for running the tests in this repository
 
-The only requirements for running the tests in this repository are Git, Make, and Docker.
+The only requirements for building and running the tests in this repository are
+Linux, Make, and [Nix](https://nix.dev/). This repository contains scripts for
+setting up a Docker container with a suitable development environment in case
+you aren't on Linux or don't want to install Nix.
 
 First, clone this repository:
 
@@ -130,22 +133,22 @@ git clone https://github.com/seL4/rust-sel4
 cd rust-sel4
 ```
 
-Next, build, run, and enter a Docker container for development:
+If you are using Docker, build, run, and enter a Docker container for
+development. This container mounts this repository's top-level at `/work`.
 
 ```
 cd hacking/docker && make run && make exec
 ```
 
-Inside the container at the repository's top-level directory, build and simulate a simple seL4-based
-system with a [root task](./crates/examples/root-task/example-root-task) written in Rust (this will
-take a few minutes):
+At this repository's top-level directory, build and simulate a simple seL4-based
+system with a [root task](./crates/examples/root-task/example-root-task) written
+in Rust (this will take a few minutes):
 
 ```
 make example
 ```
 
-Also inside the container at the repository's top-level directory, build and run all of this
-repository's automated tests:
+Build and run all of this repository's automated tests:
 
 ```
 make run-tests

hacking/binary-cache/fragment.nix.conf

@@ -0,0 +1,8 @@
+#
+# Copyright 2023, Colias Group, LLC
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+extra-substituters = https://coliasgroup.cachix.org
+extra-trusted-public-keys = coliasgroup.cachix.org-1:vYRVaHS5FCjsGmVVXlzF5LaIWjeEK17W+MHxK886zIE=