add steps readme

Author: Eyal-Danieli

steps/README.md

@@ -1,10 +1,14 @@
+# Steps
 
+Custom steps are individual execution units that are executed as part of a graph. 
+Each step has its own execution context and can run with different settings.
 
+To learn how to build and use custom steps, see: https://docs.mlrun.org/en/stable/serving/writing-custom-steps.html
 
 ## Catalog
 
 <!-- AUTOGEN:START (do not edit below) -->
 | Name | Description | Class Name | Categories |
 | --- | --- | --- | --- |
 | [verify_schema](https://github.com/mlrun/functions/tree/development/steps/src/verify_schema) | Verifies the event is aligned with the provided schema | VerifySchema | data-preparation, model-serving, utilities |
-<!-- AUTOGEN:END -->
+<!-- AUTOGEN:END -->