docs: update docs

Author: 0xnigir1

apps/processing/.env.example

@@ -18,4 +18,7 @@ COINGECKO_API_TYPE=demo
 RETRY_MAX_ATTEMPTS=3
 RETRY_BASE_DELAY_MS=3000
 RETRY_FACTOR=2
-RETRY_MAX_DELAY_MS=300000
+RETRY_MAX_DELAY_MS=300000
+
+NOTIFIER_PROVIDER=# 'slack' or 'null'
+SLACK_WEBHOOK_URL=

packages/shared/README.md

@@ -39,3 +39,13 @@ You can import the package in your TypeScript files as follows:
 ```typescript
 import { ILogger, ProcessorEvent, stringify } from "@grants-stack-indexer/shared";
 ```
+
+### Configuring the Notifier
+
+#### Slack
+
+Visit [Slack API docs](https://api.slack.com/messaging/webhooks) to create a Slack app and get a webhook URL. Follow the instructions for setting up a Slack app and get a webhook URL. Also, you can further customize the bot name, icons and scopes.
+
+#### Null
+
+The null notifier is a no-op notifier that does nothing. It is useful when you want to disable notifications.