Update gitignore.

It turns out, gitignore was configured to ignore the pre- and post- init files.
Those same files contain quite a lot of useful setup that are unique to the
dotfiles in this repo.

post-init.el

@@ -0,0 +1,40 @@
+;;; post-init.el --- This file is loaded after init.el. -*- no-byte-compile: t; lexical-binding: t; -*-
+
+;; Use straight.el for package management, integrate with use-package.
+(setq straight-use-package-by-default t)
+
+(defvar bootstrap-version)
+(let ((bootstrap-file
+       (expand-file-name
+        "straight/repos/straight.el/bootstrap.el"
+        (or (bound-and-true-p straight-base-dir)
+            user-emacs-directory)))
+      (bootstrap-version 7))
+  (unless (file-exists-p bootstrap-file)
+    (with-current-buffer
+        (url-retrieve-synchronously
+         "https://raw.githubusercontent.com/radian-software/straight.el/develop/install.el"
+         'silent 'inhibit-cookies)
+      (goto-char (point-max))
+      (eval-print-last-sexp)))
+  (load bootstrap-file nil 'nomessage))
+
+;; The compile-angel package automatically byte-compiles and
+;; native-compiles Emacs Lisp libraries. It should be loaded before
+;; any other package.
+(use-package compile-angel
+  :demand t
+  :custom
+  (compile-angel-verbose nil)
+  :config
+  (compile-angel-on-load-mode)
+  (add-hook 'emacs-lisp-mode-hook #'compile-angel-on-save-local-mode))
+
+;; Load the configs from plug-in files.
+(let ((config-dir (concat minimal-emacs-user-directory ".config.d")))
+  (if (not (file-exists-p config-dir))
+      (make-directory config-dir))
+  (dolist (lisp-file (directory-files config-dir t directory-files-no-dot-files-regexp))
+    (load lisp-file nil 'nomessage)))
+
+;;; post-init.el ends here