Document FN_FUNDING_MANIFESTS, which CONFIGURATION.md promises to list

check-configuration-doc.py failed the PR: that file says it lists every
variable the relay reads, and the new one was missing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/CONFIGURATION.md

@@ -423,6 +423,7 @@ address.
 | `FN_FEDERATION_SCREEN` | unset | Advisory IP screening for federated peers. It does not gate federation; the allowlist and the pinned key do. |
 | `FN_CONTACT_EMAIL` | unset, then `FN_REPORTS_TO` | Who runs this relay, on the contact, safety and terms pages and in `/.well-known/security.txt`. Nothing on those pages is a literal: an unconfigured relay says no address is published instead of naming somebody else. |
 | `FN_CONTACT_SUPPORT`, `FN_CONTACT_ABUSE`, `FN_CONTACT_SECURITY`, `FN_CONTACT_PRIVACY`, `FN_CONTACT_LEGAL`, `FN_CONTACT_POSTMASTER` | `FN_CONTACT_EMAIL` | One role at a time, for an operator who keeps separate mailboxes. |
+| `FN_FUNDING_MANIFESTS` | unset | The `funding.json` manifests this domain vouches for, whitespace or comma separated, served at `/.well-known/funding-manifest-urls`. Anything not starting with `https://` is dropped. Unset, that path is a 404: the manifest carries an operator's legal name, contact address and bank details, so a relay somebody else runs must not tell a funder that donations for it reach us. |
 | `FN_ANDROID_VERSION_CODE`, `FN_ANDROID_VERSION_NAME` | unset | The Android build the download page and `/api/android/release` advertise. Both are required for either to appear: a version name with no code is not a release anyone can check. |
 | `FN_ANDROID_SHA256` | unset | The APK's checksum, published so somebody can verify what they downloaded. |
 | `FN_ANDROID_NOTES` | empty | Release notes for that build. |