Document the pleroma.emoji task

docs/config/custom_emoji.md

 # Custom Emoji
 
+Before you add your own custom emoji, check if they are available in an existing pack.
+See `Mix.Tasks.Pleroma.Emoji` for information about emoji packs.
+
 To add custom emoji:
-* Add the image file(s) to `priv/static/emoji/custom`
-* In case of conflicts: add the desired shortcode with the path to `config/custom_emoji.txt`, comma-separated and one per line
-* Force recompilation (``mix clean && mix compile``)
+* Create the `STATIC-DIR/emoji/` directory if it doesn't exist
+  (`STATIC-DIR` is configurable, `instance/static/` by default)
+* Create a directory with whatever name you want (custom is a good name to show the purpose of it).
+  This will create a local emoji pack.
+* Put your `.png` emoji files in that directory. In case of conflicts, you can create an `emoji.txt`
+  file in that directory and specify a custom shortcode using the following format:
+  `shortcode, file-path, tag1, tag2, etc`. One emoji per line. Note that if you do so,
+  you'll have to list all other emojis in the pack too.
+* Either restart pleroma or connect to the iex session pleroma's running and
+  run `Pleroma.Emoji.reload/0` in it.
 
 Example:
 
-image files (in `/priv/static/emoji/custom`): `happy.png` and `sad.png`
+image files (in `instance/static/emoji/custom`): `happy.png` and `sad.png`
 
-content of `config/custom_emoji.txt`:
+content of `emoji.txt`:
 ```
 happy, /emoji/custom/happy.png, Tag1,Tag2
 sad, /emoji/custom/sad.png, Tag1

lib/mix/tasks/pleroma/emoji.ex

@@ -5,8 +5,50 @@
 defmodule Mix.Tasks.Pleroma.Emoji do
   use Mix.Task
 
-  @shortdoc "Manages Pleroma instance"
+  @shortdoc "Manages emoji packs"
   @moduledoc """
+  Manages emoji packs
+
+  ## ls-packs
+
+  mix pleroma.emoji ls-packs [OPTION...]
+
+  Lists the emoji packs and metadata specified in the manifest.
+
+  ### Options
+
+  - `-m, --manifest PATH/URL` - path to a custom manifest, it can either be an URL
+    starting with `http`, in that case the manifest will be fetched from that address,
+    or a local path
+
+  ## get-packs
+
+  mix pleroma.emoji get-packs [OPTION...] PACKS
+
+  Fetches, verifies and installs the specified PACKS from the manifest into
+  the `STATIC-DIR/emoji/PACK-NAME
+
+  ### Options
+
+  - `-m, --manifest PATH/URL` - same as ls-packs
+
+  ## gen-pack
+
+  mix pleroma.emoji gen-pack PACK-URL
+
+  Creates a new manifest entry and a file list from the specified remote pack file.
+  Currently, only .zip archives are recognized as remote pack files and packs are therefore
+  assumed to be zip archives. This command is intended to run interactively and
+  will first ask you some basic questions about the pack, then download the remote
+  file and generate an MD5 signature for it, then generate an emoji file list for you.
+
+  The manifest entry will either be written to a newly created `index.json` file or appended to the existing one,
+  *replacing* the old pack with the same name if it was in the file previously.
+
+  The file list will be written to the file specified previously, *replacing* that file.
+  You _should_ check that the file list doesn't contain anything you don't need in the pack, that is,
+  anything that is not an emoji (the whole pack is downloaded, but only emoji files are extracted).
+
   """
 
   @default_manifest Pleroma.Config.get!([:emoji, :default_manifest])