Update install instructions

[ambergrimaldi-bcm]

Describe the bug

The current instructions listed here https://github.com/vmware-samples/nsx-t/blob/master/python/README.md are incorrect and cause dependency errors on install.

Reproduction steps

1. Make sure python is installed on system
2. download the following files from https://developer.broadcom.com/sdks/vmware-nsx-for-python/latest:
   nsx_global_policy_python_sdk-9.0.1-py2.py3-none-any.whl
   nsx_policy_python_sdk-9.0.1-py2.py3-none-any.whl
   nsx_python_sdk-9.0.1-py2.py3-none-any.whl
   vapi_common-2.61.2-py3-none-any.whl
   vmware_vapi_common_client-2.61.2-py3-none-any.whl
   vmware_vapi_runtime-2.61.2-py3-none-any.whl
3. Using pip install the .whl files
4. even when installing vmware_vapi_runtime-2.61.2-py3-none-any.whl first, when installing vapi_common-2.61.2-py3-none-any.whl you receive the following error
   ERROR: Could not find a version that satisfies the requirement vapi-runtime==2.61.2

Expected behavior

Expected behavior is for there to not be dependency errors based off install instructions provided.

Additional context

For step 3 under the section "To install the SDK and its dependencies, issue the following commands" it needs to be adjusted to the following:

# 3) Copy the NSX-T SDKs and vapi runtime:
# Navigate to https://developer.broadcom.com/sdks/vmware-nsx-for-python/latest
# Adjust the version drop down on the right side to the appropriate version
# Copy the following list of SDK files to the lib directory in this repo:
# nsx_global_policy_python_sdk-9.0.1-py2.py3-none-any.whl
# nsx_policy_python_sdk-9.0.1-py2.py3-none-any.whl
# nsx_python_sdk-9.0.1-py2.py3-none-any.whl
# vmware_vapi_common_client-2.61.2-py3-none-any.whl
# vmware_vapi_runtime-2.61.2-py3-none-any.whl

The reason is the vapi_common .whl file is no longer needed as of NSX 9. The only required .whl files are vmware_vapi_common_client-2.61.2-py3-none-any.whl and vmware_vapi_runtime-2.61.2-py3-none-any.whl