Add config doc

docs/config.md

@@ -210,3 +210,8 @@ curl "http://localhost:4000/api/pleroma/admin/invite_token?admin_token=somerando
 * `max_jobs`: The maximum amount of parallel federation jobs running at the same time.
 * `initial_timeout`: The initial timeout in seconds
 * `max_retries`: The maximum number of times a federation job is retried
+
+## Pleroma.Web.Metadata
+* `providers`: a list of metadata providers to enable. Providers avalible:
+  * Pleroma.Web.Metadata.Providers.OpenGraph
+  * Pleroma.Web.Metadata.Providers.TwitterCard

lib/pleroma/web/metadata.ex

@@ -1,7 +1,7 @@
 defmodule Pleroma.Web.Metadata do
   alias Phoenix.HTML
 
-  @parsers Pleroma.Config.get([:metadata, :providers], [])
+  @providers Pleroma.Config.get([__MODULE__, :providers], [])
   def get_cached_tags(%{activity: activity, user: user} = params) do
     # We don't need to use the both activity and a user since the object can't change it's content
     key = "#{:erlang.term_to_binary(user)}#{activity.data["id"]}"
@@ -29,7 +29,7 @@ def get_cached_tags(params) do
   end
 
   def build_tags(params) do
-    Enum.reduce(@parsers, "", fn parser, acc ->
+    Enum.reduce(@providers, "", fn parser, acc ->
       rendered_html =
         params
         |> parser.build_tags()