subtree(users/wpcarro): docking briefcase at '24f5a642'

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c
git-subtree-split: 24f5a642af
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

users/wpcarro/emacs/README.md

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+# Emacs
+
+Emacs is one of a handful software projects that I highly value. I consider it
+as central to my workflow as `git` and `nix`.
+
+## Installing
+
+If you already have `briefcase` on your local file system, run the following
+from the top-level `briefcase` directory:
+
+```shell
+$ nix-build -f . -iA emacs.nixos
+```