YAML documentation: node id and endpoint defaults

Author: cecille

docs/testing/yaml.md

@@ -293,6 +293,11 @@ All YAML tests assume that the DUT has previously been commissioned before
 running. DUTs should be commissioned using chip-tool. Use the same KVS file when
 running the test.
 
+By default, the tests use node ID 0x12344321. The easiest way to run the tests
+is to commission with this node ID. Alternately, you can change the target node
+ID on the command line, as shown in the [Running the tests](#running-the-tests)
+section.
+
 #### Running the tests
 
 There are several options for running tests locally. Because the YAML runner
@@ -338,6 +343,10 @@ with --
 
 ```
 
+Each test defines a default endpoint to target. Root node cluster tests run
+against endpoint 0 by default. Most other cluster tests run against endpoint 1.
+You can set the endpoint for the test using the `endpoint` config variable.
+
 #### Factory resetting the DUT
 
 On the host machine, you can simulate a factory reset by deleting the KVS file.