Move stuff from readme

Creating-packs.md

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+In addition to the sticker picker widget itself, this project includes some
+utility scripts you can use to import and create sticker packs.
+
+To get started, install the dependencies for using the commands:
+
+0. Make sure you have Python 3.6 or higher.
+1. (Optional) Set up a virtual environment.
+   1. Create with `virtualenv -p python3 .venv`
+   2. Activate with `source .venv/bin/activate`
+2. Install the utility commands and their dependencies with `pip install .`
+
+## Importing packs from Telegram
+To import packs from Telegram, simply run `sticker-import <pack urls...>` with
+one or more t.me/addstickers/... URLs.
+
+If you want to list the URLs of all your saved packs, use `sticker-import --list`.
+This requires logging in with your account instead of a bot token.
+
+Notes:
+
+* On the first run, it'll prompt you to log in to Matrix and Telegram.
+ * The Matrix URL and access token are stored in `config.json` by default.
+ * The Telethon session data is stored in `sticker-import.session` by default.
+* By default, the pack data will be written to `web/packs/`.
+* You can pass as many pack URLs as you want.
+* You can re-run the command with the same URLs to update packs.
+
+## Creating your own packs
+1. Create a directory with your sticker images.
+   * The file name (excluding extension) will be used as the caption.
+   * The directory name will be used as the pack name/ID.
+   * If you want the stickers to appear in a specific order, prefix them with
+     `number-`, e.g. `01-Cat.png`. The number and dash won't be included in the
+     caption.
+2. Run `sticker-pack <pack directory>`.
+   * If you want to override the pack displayname, pass `--title <custom title>`.
+   * Pass `--add-to-index web/packs/` if you want to automatically add the
+     generated pack to your sticker picker.