configurations: add VENDOR guidelines

In order to allow configurations to be arranged in subdirectories
for vendors, some guidelines are proposed on who is a vendor.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I1e5f329ddd5066b2226077c9930488927358abd1
diff --git a/.prettierignore b/.prettierignore
index 6a9364a..a466900 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -1 +1,2 @@
 configurations/*
+!configurations/**/*.md