Update readme.python.md (#15226)

Author: RAY-316

specification/iothub/resource-manager/readme.python.md

@@ -20,6 +20,7 @@ Generate all API versions currently shipped for this package
 
 ```yaml $(python) && $(multiapi) && $(track2)
 batch:
+  - tag: package-2021-07
   - tag: package-2021-03
   - tag: package-preview-2021-03
   - tag: package-2020-03
@@ -40,6 +41,16 @@ clear-output-folder: false
 perform-load: false
 ```
 
+### Tag: package-2021-07 and python
+
+These settings apply only when `--tag=package-2021-07 --python` is specified on the command line.
+Please also specify `--python-sdks-folder=<path to the root directory of your azure-sdk-for-python clone>`.
+
+``` yaml $(tag) == 'package-2021-07' && $(python)
+namespace: azure.mgmt.iothub.v2021_07_01
+output-folder: $(python-sdks-folder)/iothub/azure-mgmt-iothub/azure/mgmt/iothub/v2021_07_01
+```
+
 ### Tag: package-2021-03 and python
 
 These settings apply only when `--tag=package-2021-03 --python` is specified on the command line.