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.

.gitignore

@@ -1,6 +1,25 @@
-*
-!README.md
-!early-init.el
-!init.el
-!.images/
-!.LICENSE
+/auto-save-list/
+/custom.el
+/easysession
+/eln-cache/
+/elpa/
+/elpaca/
+/etc/
+/history
+/ielm-history.eld
+/lisp/
+/projectile-bookmarks.eld
+/recentf
+/saveplace
+/tramp
+/straight/
+/themes/
+/transient/
+/tree-sitter/
+/undo-fu-session/
+/var/
+/bookmarks
+/bookmarks
+/ido.last
+/autosave/
+/url/