Bring setup steps back to README.

README.md

@@ -1,36 +1,37 @@
 [![Build status](https://github.com/schmonz/junit-greencently/actions/workflows/main-build.yml/badge.svg)](https://github.com/schmonz/junit-greencently/actions/workflows/main-build.yml)
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.schmonz/junit-greencently/badge.svg?gav=true)](https://central.sonatype.com/artifact/com.schmonz/junit-greencently)
 
-# Greencently
-
-For teams whose commits fail on red tests, Greencently offers an optimization:
-the pre-commit hook can know when you've run all tests green "recently enough".
-Team chooses policy.
-
-## Benefits (immediate)
-
-- Lower-friction commits
-- Time and energy saved
-
-## Benefits (speculative)
-
-Probably you'll lean into smaller, more frequent commits.
-Maybe you'll also feel more able to invest in further test speedups.
-
-## Usage
-
-Nobody needs to learn anything.
-The pre-commit hook still has your back when you forget to...
-
-- Run any tests
-- Run all tests
-- Attend to red tests
-
-With Greencently, the pre-commit hook also has your back when you _remember_.
-
-All tests green, recently?
-Commit quickly and stay in flow.
+# [Greencently](https://schmonz.com/software/greencently)
 
 ## Setup
 
-- [Documentation](https://schmonz.com/software/greencently)
+For JUnit 5:
+
+1. Update `build.gradle.kts`:
+```gradle
+dependencies {
+    testRuntimeOnly("com.schmonz:junit-greencently:VERSION_NUMBER_HERE")
+}
+tasks.withType<Test> {
+    jvmArgs("-Djunit.jupiter.extensions.autodetection.enabled=true")
+    maxParallelForks = 1  // see #4
+}
+```
+2. Run all tests for project
+3. If green, observe top-level `.when-all-tests-were-green-junit5`
+4. Append to top-level `.gitignore`: `*when-all-tests-were-green*`
+5. In pre-commit hook, inspect file modification time. Example:
+```sh
+#!/bin/sh
+all_tests_were_recently_green() {
+    thenstamp=$(date -r .when-all-tests-were-green-junit5 '+%s' 2>/dev/null || echo 0)
+    nowstamp=$(date '+%s')
+    secondsago=$(expr ${nowstamp} - ${thenstamp})
+    [ ${secondsago} -lt 30 ]
+}
+if all_tests_were_recently_green; then
+    ./gradlew clean build -x test
+else
+    ./gradlew clean build
+fi
+```