Add Streaming Specs in PROTOCOL in branch 0.6 (#414)

* Add Streaming Specs

* resolve comments

* add a

PROTOCOL.md

@@ -34,6 +34,7 @@
     - [Per-file Statistics](#per-file-statistics)
   - [SQL Expressions for Filtering](#sql-expressions-for-filtering)
   - [JSON predicates for Filtering](#json-predicates-for-filtering)
+  - [Delta Sharing Streaming Specs](#delta-sharing-streaming-specs)
 - [Profile File Format](#profile-file-format)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
@@ -2913,6 +2914,24 @@ Examples
 }
 ```
 
+## Delta Sharing Streaming Specs
+Delta Sharing Streaming is supported starting from delta-sharing-spark 0.6.0. As it's implemented
+based on spark structured streaming, it leverages a pull model to consume the new data of the shared
+table from the delta sharing server. In addition to most options supported in delta streaming,
+there are two options/spark configs for delta sharing streaming.
+
+- spark config **spark.delta.sharing.streaming.queryTableVersionIntervalSeconds**: DeltaSharingSource
+  leverages [getTableVersion](#query-table-version) rpc to check whether there is new data available
+  to consume. In order to reduce the traffic burden to the delta sharing server, there's a minimum 30
+  seconds interval between two getTableVersion rpcs to the delta sharing server. Though, if you are ok
+  with less freshness on the data and want to reduce the traffic to the server, you can set this
+  config to a larger number, for example: 60s or 120s. An error will be thrown if it's set less than 30 seconds.
+- option **maxVersionsPerRpc**: DeltaSharingSource leverages [QueryTable](#read-data-from-a-table)
+  rpc to continuously read new data from the delta sharing server. There might be too much
+  new data to be returned from the server if the streaming has paused for a while on the recipient
+  side. Its default value is 100, a smaller number is recommended such as `.option("maxVersionsPerRpc", 10)`
+  to reduce the traffic load for each rpc. This shouldn't affect the freshness of the data significantly
+  assuming the process time of the delta sharing server grows linearly with `maxVersionsPerRpc`.
 
 # Profile File Format