Add BookWyrm user-agent to http requests

This allows other software to identify BookWyrm in calls, as well as
will allow BookWyrm to differentiate between calls done from other
fediverse software and BookWyrm to answer with specific BookWyrm data.

bookwyrm/settings.py

@@ -3,6 +3,8 @@ import os
 
 from environs import Env
 
+import requests
+
 env = Env()
 DOMAIN = env('DOMAIN')
 
@@ -150,3 +152,7 @@ STATIC_URL = '/static/'
 STATIC_ROOT = os.path.join(BASE_DIR, env('STATIC_ROOT', 'static'))
 MEDIA_URL = '/images/'
 MEDIA_ROOT = os.path.join(BASE_DIR, env('MEDIA_ROOT', 'images'))
+
+USER_AGENT = "%s (BookWyrm/%s; +https://%s/)" % (requests.utils.default_user_agent(),
+        "0.1", # TODO: change 0.1 into actual version
+        DOMAIN)