update mixedreality readme.java.md (Azure#12778)

specification/mixedreality/resource-manager/readme.java.md

@@ -16,9 +16,23 @@ output-folder: $(azure-libraries-for-java-folder)/azure-mgmt-mixedreality
 
 ``` yaml $(java) && $(multiapi)
 batch:
+  - tag: package-2021-01
   - tag: package-2020-05
 ```
 
+### Tag: package-2021-01 and java
+
+These settings apply only when `--tag=package-2021-01 --java` is specified on the command line.
+Please also specify `--azure-libraries-for-java-folder=<path to the root directory of your azure-sdk-for-java clone>`.
+
+``` yaml $(tag) == 'package-2021-01' && $(java) && $(multiapi)
+java:
+  namespace: com.microsoft.azure.management.mixedreality.v2021_01_01
+  output-folder: $(azure-libraries-for-java-folder)/sdk/mixedreality/mgmt-v2021_01_01
+regenerate-manager: true
+generate-interface: true
+```
+
 ### Tag: package-2020-05 and java
 
 These settings apply only when `--tag=package-2020-05 --java` is specified on the command line.