feat(docs): Add documents for the two bufferSize configs.

docs/server_guide.md

@@ -116,6 +116,10 @@ This document will introduce how to deploy Uniffle shuffle servers.
 | rss.server.storage.audit.log.enabled | false | When set to true, for auditing purposes, the server will log audit records for every disk write and delete operation. Each file write is logged, while delete operations are specific to application ID/shuffle ID, removing all associated files and recording the deletion of the entire application ID or shuffle ID. For a write operation, it includes the size of the data written, the storage type and the specific disk to which it is written. It will be disabled by default. |
 | rss.server.rpc.audit.log.enabled | true | When set to true, for auditing purposes, the server will log audit records for every rpc request operation. |
 | rss.server.rpc.audit.log.excludeList | appHeartbeat | Exclude record rpc audit operation list, separated by ','. |
+| rss.storage.localfile.write.dataBufferSize | 8K | The size of the buffer used to cache data written for LOCALFILE. |
+| rss.storage.localfile.write.indexBufferSize | 8K | The size of the buffer used to cache index written for LOCALFILE. |
+| rss.storage.hdfs.write.dataBufferSize | 8K | The size of the buffer used to cache data written for HDFS. |
+| rss.storage.hdfs.write.indexBufferSize | 8K | The size of the buffer used to cache index written for HDFS. |
 
 ### Advanced Configurations
 | Property Name | Default | Description |