Update ex_doc, add llms.txt support, update description

Author: FelonEkonom

mix.exs

@@ -1,7 +1,7 @@
 defmodule Membrane.RTP.H264.MixProject do
   use Mix.Project
 
-  @version "0.20.4"
+  @version "0.20.5"
   @github_url "https://github.com/membraneframework/membrane_rtp_h264_plugin"
 
   def project do
@@ -22,7 +22,8 @@ defmodule Membrane.RTP.H264.MixProject do
       name: "Membrane RTP H264 Plugin",
       source_url: @github_url,
       docs: docs(),
-      homepage_url: "https://membrane.stream"
+      homepage_url: "https://membrane.stream",
+      aliases: [docs: ["docs", &prepend_llms_links/1]]
     ]
   end
 
@@ -40,7 +41,6 @@ defmodule Membrane.RTP.H264.MixProject do
     [
       main: "readme",
       extras: ["README.md", "LICENSE"],
-      formatters: ["html"],
       source_ref: "v#{@version}",
       nest_modules_by_prefix: [
         Membrane.RTP.H264
@@ -66,7 +66,7 @@ defmodule Membrane.RTP.H264.MixProject do
       {:membrane_rtp_format, "~> 0.11.0"},
       {:bunch, "~> 1.5"},
       # Dev
-      {:ex_doc, ">= 0.0.0", only: :dev, runtime: false},
+      {:ex_doc, "~> 0.40", only: :dev, runtime: false},
       {:dialyxir, ">= 0.0.0", only: :dev, runtime: false},
       {:credo, ">= 0.0.0", only: :dev, runtime: false}
     ]
@@ -84,4 +84,16 @@ defmodule Membrane.RTP.H264.MixProject do
       opts
     end
   end
-end
+
+  defp prepend_llms_links(_) do
+    path = "doc/llms.txt"
+
+    if File.exists?(path) do
+      existing = File.read!(path)
+
+      header = "- [Membrane Core](https://hexdocs.pm/membrane_core/llms.txt)\n\n"
+
+      File.write!(path, header <> existing)
+    end
+  end
+end