add internal/external information in author meta

Author: fcmsilva

authors/singlestore.toml

@@ -1,3 +1,4 @@
 name="SingleStore"
 description="Engineering Team"
 logo="singlestore"
+external=false

resources/author-check.py

@@ -21,6 +21,9 @@ def check_author(author_path):
         if 'description' not in meta:
             error(f'No `description` in `meta` section of {author_path}')
 
+        if 'external' not in meta:
+            error(f'No `external` in `meta` section of {author_path}')
+
         # Logo is optional, but if defined a corresponding image must exist
         if 'logo' in meta:
             logo_id = meta['logo']