Add podroll endpoint integration and env docs

.env.example

@@ -0,0 +1,11 @@
+# Optional Podroll endpoint settings
+# Default mount path in indiekit.config.mjs is /podrollapi
+PODROLL_MOUNT_PATH=/podrollapi
+
+# FreshRSS greader API URL for episode sync
+# Example: https://freshrss.example/api/query.php?user=USER&t=TOKEN&f=greader
+PODROLL_EPISODES_URL=
+
+# FreshRSS OPML export URL for source sync
+# Example: https://freshrss.example/api/query.php?user=USER&t=TOKEN&f=opml
+PODROLL_OPML_URL=