[hotfix] [docs] Fix a typo in index.md

This closes apache#6193.

docs/index.md

@@ -31,7 +31,7 @@ Apache Flink is an open source platform for distributed stream and batch data pr
 
 ## First Steps
 
-- **Concepts**: Start with the basic concepts of Flink's [Dataflow Programming Model](concepts/programming-model.html) and [Distributed Runtime Environment](concepts/runtime.html). This will help you understand other parts of the documentation, including the setup and programming guides. We recommended you read these sections first.
+- **Concepts**: Start with the basic concepts of Flink's [Dataflow Programming Model](concepts/programming-model.html) and [Distributed Runtime Environment](concepts/runtime.html). This will help you understand other parts of the documentation, including the setup and programming guides. We recommend you read these sections first.
 
 - **Quickstarts**: [Run an example program](quickstart/setup_quickstart.html) on your local machine or [study some examples](examples/index.html).