+readme add more info about the sanity script to the contributing readme (#57)

Author: ktoso

CONTRIBUTING.md

@@ -68,6 +68,31 @@ We require that your commit messages match our template. The easiest way to do t
 SwiftServiceLifecycle uses XCTest to run tests on both macOS and Linux. While the macOS version of XCTest is able to use the Objective-C runtime to discover tests at execution time, the Linux version is not.
 For this reason, whenever you add new tests **you have to run a script** that generates the hooks needed to run those tests on Linux, or our CI will complain that the tests are not all present on Linux. To do this, merely execute `ruby ./scripts/generate_linux_tests.rb` at the root of the package and check the changes it made.
 
+### Run `./scripts/sanity.sh`
+
+The scripts directory contains a [sanity.sh script](https://github.com/swift-server/swift-service-lifecycle/blob/master/scripts/sanity.sh) 
+that enforces additional checks, like license headers and formatting style.
+Please make sure to `./scripts/sanity.sh` before pushing a change upstream, otherwise it is likely the PR validation will fail
+on minor changes such as a missing `self.` or similar formatting issues.
+
+> The script also executes the above mentioned `generate_linux_tests.rb`.
+
+For frequent contributors, we recommend adding the script as a [git pre-push hook](https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks), which you can do via executing the following command
+in the project root directory: 
+
+```bash
+cat << EOF > .git/hooks/pre-push
+#!/bin/bash
+
+if [[ -f "scripts/sanity.sh" ]]; then
+  scripts/sanity.sh
+fi
+EOF
+```
+Which makes the script execute, and only allow the `git push` to complete if the check has passed.
+
+In the case of formatting issues, you can then `git add` the formatting changes, and attempt the push again. 
+
 ## How to contribute your work
 
 Please open a pull request at https://github.com/swift-server/swift-service-lifecycle. Make sure the CI passes, and then wait for code review.

README.md

@@ -6,7 +6,7 @@ It also provides a `Signal`-based shutdown hook, to shut down on signals like `T
 Swift Service Lifecycle was designed with the idea that every application has some startup and shutdown workflow-like-logic which is often sensitive to failure and hard to get right.
 The library codes this common need in a safe and reusable way that is non-framework specific, and designed to be integrated with any server framework or directly in an application.
 
-This is the beginning of a community-driven open-source project actively seeking contributions, be it code, documentation, or ideas. What Swift Service Lifecycle provides today is covered in the [API docs](https://swift-server.github.io/swift-service-lifecycle/), but it will continue to evolve with community input.
+This is the beginning of a community-driven open-source project actively seeking [contributions](CONTRIBUTING.md), be it code, documentation, or ideas. What Swift Service Lifecycle provides today is covered in the [API docs](https://swift-server.github.io/swift-service-lifecycle/), but it will continue to evolve with community input.
 
 ## Getting started