[wip] emacsPackages: add README.md

For now it has documentation for bulk updaters.

pkgs/applications/editors/emacs/elisp-packages/README.md

@@ -0,0 +1,62 @@
+# Emacs Lisp Packages Framework
+
+This directory includes a framework for packaging Emacs Lisp (henceforth, Elisp)
+packages to Nixpkgs.
+
+## Bulk Updating
+
+We have the following scripts:
+
+- `update-scripts_library.sh`
+
+  This file serves as a library, containing useful functions to deal with bulk updates.
+  It can be `source`'d in both interactive and batch environments.
+
+  This library provides the following functions:
+
+  - `download_packageset`
+
+    This function downloads from [`nix-community` Emacs Overlay](https://github.com/nix-community/emacs-overlay) the corresponding files.
+
+    It accepts one argument.
+    This argument can assume one of the following values:
+    `elpa`, `elpa-devel`,  `melpa`, `melpa-stable`, `nongnu`, `nongnu-devel`.
+
+  - `test_packageset`
+
+    This function runs a simple test that instantiates the corresponding package set.
+
+    It accepts one argument.
+    This argument can assume one of the following values:
+    `elpa`, `elpa-devel`,  `melpa`, `melpa-stable`, `nongnu`, `nongnu-devel`.
+
+  - `commit_packageset`
+
+    This function commits the corresponding package set to the Nixpkgs repository, writing a one-line descriptive commit message.
+
+    It accepts two arguments.
+
+    The first argument can assume one of the following values: `elpa`,
+    `elpa-devel`, `melpa`, `melpa-stable`, `nongnu`, `nongnu-devel`.
+    The second argument is an optional free-form string used verbatim, describing the origin of the change being committed.
+    Its default value is `interactive session`.
+
+- `update-package-sets`
+
+  This script updates the package sets passed to it as arguments.
+
+  It accepts multiple arguments.
+  Each argument can assume one of the following values:
+  `elpa`, `elpa-devel`, `nongnu`, `nongnu-devel`.
+
+- `update-melpa`
+
+  This script updates `recipes-archive-melpa.json`, a JSON file that describes the MELPA package set.
+
+  It accepts no arguments.
+
+- `update-from-overlay`
+
+  This script downloads all the packagesets from overlay, then tests and commits them.
+
+  It accepts no arguments.