Add TiDB/TiKV/PD version and Spark version supported for each latest …

…major release (pingcap#804)

README.md

@@ -51,6 +51,28 @@ mvn clean install -Dmaven.test.skip=true -P spark-2.4
 
 Remember to add `-Dmaven.test.skip=true` to skip all the tests if you don't need to run them.
 
+## Maximum TiDB/TiKV/PD version supported by TiSpark
+
+Each latest TiSpark version guarantees *backward compatibility* for TiDB components, i.e., supports TiDB/TiKV/PD until a certain release. Its reason varies, amongst which the most common one is that the new features and bug-fixes provided by TiDB components requires update on API, dependencies, etc.
+
+| TiSpark Version | Maximum TiDB Version | Maximum TiKV Version | Maximum PD Version |
+| ----- | ------ | ------ | ------ |
+| < 1.2 | v2.1.4 | v2.1.4 | v2.1.4 |
+| 1.2 | v2.1.x | v2.1.x | v2.1.x |
+| 2.x | v3.0.0-beta | v3.0.0-beta | v3.0.0-beta |
+| Latest (master) | Latest | Latest | Latest |
+
+## Available Spark version supported by TiSpark
+
+While TiSpark provides downward compatibility for TiDB, it guarantees **restricted** Spark version support for means of catching up to the latest Datasource API changes.
+
+| TiSpark Version | Spark Version |
+| ----- | ------ |
+| 1.x | Spark v2.1.0+ |
+| 2.0 | Spark v2.3.0+ |
+| 2.1 | Spark v2.3.0+, Spark v2.4.0+ |
+| Latest (master) | Spark v2.3.0+, Spark v2.4.0+ |
+
 ## How to migrate from Spark 2.1 to Spark 2.3/2.4
 For users using Spark 2.1 who wish to migrate to latest TiSpark on Spark 2.3/2.4, please download or install Spark 2.3+/2.4+ following instructions on [Apache Spark Site](http://spark.apache.org/downloads.html) and overwrite the old spark version in `$SPARK_HOME`.