Update config v2 doc

docs/en_US/Tutorial/ExperimentConfig.rst

@@ -1,5 +1,7 @@
-Experiment Config Reference
-===========================
+Experiment Config Reference (legacy)
+====================================
+
+This is the previous version (V1) of experiment configuration specification. It is still supported for now, but we recommend users to use `the new version of experiment configuration (V2) <../reference/experiment_config.rst>`_.
 
 A config file is needed when creating an experiment. The path of the config file is provided to ``nnictl``.
 The config file is in YAML format.

docs/en_US/Tutorial/QuickStart.rst

@@ -149,6 +149,9 @@ Three steps to start an experiment
      codeDir: .
      gpuNum: 0
 
+
+.. _nniignore:
+
 .. Note:: If you are planning to use remote machines or clusters as your :doc:`training service <../TrainingService/Overview>`, to avoid too much pressure on network, we limit the number of files to 2000 and total size to 300MB. If your codeDir contains too many files, you can choose which files and subfolders should be excluded by adding a ``.nniignore`` file that works like a ``.gitignore`` file. For more details on how to write this file, see the `git documentation <https://git-scm.com/docs/gitignore#_pattern_format>`__.
 
 *Example:* :githublink:`config.yml <examples/trials/mnist-pytorch/config.yml>` and :githublink:`.nniignore <examples/trials/mnist-pytorch/.nniignore>`

docs/en_US/reference.rst

@@ -5,8 +5,8 @@ References
     :maxdepth: 2
 
     nnictl Commands <Tutorial/Nnictl>
-    Experiment Configuration <Tutorial/ExperimentConfig>
-    Experiment Configuration V2 <reference/experiment_config>
+    Experiment Configuration <reference/experiment_config>
+    Experiment Configuration (legacy) <Tutorial/ExperimentConfig>
     Search Space <Tutorial/SearchSpaceSpec>
     NNI Annotation <Tutorial/AnnotationSpec>
     SDK API References <sdk_reference>