specific branch version of `git clone` (#2659)

docs/en_US/NAS/Benchmarks.md

@@ -21,9 +21,11 @@ To avoid storage and legality issues, we do not provide any prepared databases.
 
 1. Clone NNI to your machine and enter `examples/nas/benchmarks` directory.
 ```
-git clone https://github.com/microsoft/nni.git
+git clone -b ${NNI_VERSION} https://github.com/microsoft/nni
 cd nni/examples/nas/benchmarks
 ```
+Replace `${NNI_VERSION}` with a released version name or branch name, e.g., `v1.7`.
+
 2. Install dependencies via `pip3 install -r xxx.requirements.txt`. `xxx` can be `nasbench101`, `nasbench201` or `nds`.
 3. Generate the database via `./xxx.sh`. The directory that stores the benchmark file can be configured with `NASBENCHMARK_DIR` environment variable, which defaults to `~/.nni/nasbenchmark`. Note that the NAS-Bench-201 dataset will be downloaded from a google drive.
 

docs/en_US/TrainingService/AMLMode.md

@@ -78,10 +78,11 @@ The required information of amlConfig could be found in the downloaded `config.j
 
 Run the following commands to start the example experiment:
 ```
-git clone https://github.com/microsoft/nni.git
+git clone -b ${NNI_VERSION} https://github.com/microsoft/nni
 cd nni/examples/trials/mnist-tfv1
 
 # modify config_aml.yml ...
 
 nnictl create --config config_aml.yml
 ```
+Replace `${NNI_VERSION}` with a released version name or branch name, e.g., `v1.7`.