add documentation

README.md

@@ -7,6 +7,30 @@ You may bring your own ZkApp Rollup implemented in any way you see fit. However,
 
 After implementing [these](rollup/src/generics.ts) abstractions, make sure to use them in the sequencer by updating [mapper.ts](sequencer/src/mapper.ts), [reducer.ts](sequencer/src/reducer.ts) [compiler.ts](sequencer/src/compiler.ts) and [sequencer.ts](sequencer/src/sequencer.ts).
 
+To start the sequencer:
+```bash
+yarn sequencer start
+```
+This starts up a grpc server which can be used to run the demos (You can call `make run-demo` to run a basic demo). You can modify the server code to fit your needs [here](sequencer/src/server/services/sequencer.ts).
+
+The core of the sequencer code is in [sequencer/src/map-reduce/](sequencer/src/map-reduce/client/client.ts). You can use it directly to run the map-reduce operation as such:
+```typescript
+const MODE = MODES.EMR
+const REGION = 'eu-central-1'
+const client = new MapReduceClient<RollupProof>(MODE, REGION);
+
+// First we need to upload your transactions to S3
+const txUploader = client.uploader.uploadTransactionsToS3();
+const transactions: MyTransaction[] = [/* ...your transactions */]
+for (const tx of transactions) {
+    txUploader.write(tx.serialize());
+}
+inputFileUrl = await txUploader.end();
+
+// Then we can initialize a Hadoop cluster and start the map-reduce operation
+const accumulatedProof = await this.mapReduce.process(inputFileUrl, transactions.length);
+```
+
 ## [Deployment](./accumulator/infra/README.md)
 TODO:  missing a general overview including explanation about deployment of the sequencer, the hadoop cluster, and instructions about terraform