docs: document multi-token campaign support (#191)

Author: joelpeace48-cell

README.md

@@ -99,6 +99,18 @@ stellar contract invoke --id $CONTRACT_ID -- update_metadata \
 
 The contract emits a `MetadataUpdated` event containing both the old and new metadata values. The backend event indexer processes this event and updates local state automatically.
 
+### Multi-token campaigns (issue #191)
+
+Campaigns can accept more than one Stellar asset code. When `acceptedTokens` contains multiple entries the frontend renders a per-token progress bar beneath the main progress bar, and the pledge form shows a token selector so contributors can choose which asset to pledge.
+
+The backend tracks per-token pledge totals in the `tokenBalances` field (a `Record<assetCode, amount>` map built from the `pledges` table grouped by `asset_code`). This is returned on every `GET /api/campaigns/:id` response and on the campaign list.
+
+**Contract side:** The Soroban contract stores `accepted_tokens: Vec<String>` on each campaign. `contribute()` validates that the pledged asset is in the list before recording the pledge.
+
+**Frontend side:** `CampaignCard` renders individual `<div class="progress-bar">` elements for each accepted token when `tokenBalances` is present. `CampaignDetailPanel` conditionally shows a `<select>` token picker above the amount field when `acceptedTokens.length > 1`.
+
+**Backend side:** `getCampaignTokenBalances(campaignId)` queries the `pledges` table grouped by `asset_code` and returns the map. `getCampaign()` populates `campaign.tokenBalances` on every read.
+
 ### Deadline extension governance (issue #192)
 
 Any existing contributor can request a deadline extension: