Add minimal document to the header of the code

melpa/melpa#5427 (comment)

Author: zonuexe

phpstan.el

@@ -26,6 +26,31 @@
 
 ;; Static analyze for PHP code using PHPStan.
 ;; https://github.com/phpstan/phpstan
+;;
+;; ## Instalation
+;;
+;; You need to get either the local PHP runtime or Docker and prepare for PHPStan.
+;; Please read the README for these details.
+;; https://github.com/emacs-php/phpstan.el/blob/master/README.org
+;;
+;; If you are a Flycheck user, activate it by selecting `phpstan`
+;; with `M-x flycheck-select-checker'.
+;;
+;; ## Directory local variables
+;;
+;; Put the following into .dir-locals.el files on the root directory of project.
+;; Each variable can read what is documented by `M-x describe-variables'.
+;;
+;;     ((nil . ((php-project-root . git)
+;;              (phpstan-executable . docker)
+;;              (phpstan-working-dir . (root . "path/to/dir"))
+;;              (phpstan-config-file . (root . "path/to/dir/phpstan-docker.neon"))
+;;              (phpstan-level . 7))))
+;;
+;; If you want to know the directory variable specification, please refer to
+;; M-x info [Emacs > Customization > Variables] or the following web page.
+;; https://www.gnu.org/software/emacs/manual/html_node/emacs/Directory-Variables.html
+;;
 
 ;;; Code:
 (require 'php-project)