added plugin git submodule definition

.github/FUNDING.yml

@@ -1,8 +0,0 @@
-# These are supported funding model platforms
-
-github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
-patreon: # Replace with a single Patreon username
-open_collective: grav
-ko_fi: # Replace with a single Ko-fi username
-tidelift: # Replace with a single Tidelift platform-name/package-name e.g., npm/babel
-custom: # Replace with a single custom sponsorship URL

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "plugin-error"]
+	path = user/plugins/error
+	url = https://github.com/getgrav/grav-plugin-error