Provide some stuff we know of for Mastodon schema

Should fix GoToSocial pulls. Refs #223.

.gitignore

@@ -15,3 +15,4 @@
 __pycache__/
 api-test.*
 notes.md
+notes.py

core/ld.py

@@ -362,7 +362,15 @@ schemas = {
         "contentType": "application/ld+json",
         "documentUrl": "http://joinmastodon.org/ns",
         "contextUrl": None,
-        "document": {},
+        "document": {
+            "@context": {
+                "toot": "http://joinmastodon.org/ns#",
+                "discoverable": "toot:discoverable",
+                "devices": "toot:devices",
+                "featured": "toot:featured",
+                "featuredTags": "toot:featuredTags",
+            },
+        },
     },
 }