update: table of contents (#8)

Co-authored-by: Yash Tibrewal <[email protected]>

Author: arvindbr8

README.md

@@ -20,6 +20,10 @@ Here is a list of available codelabs in this repository:
 
 - [Getting Started with gRPC-Go](codelabs/Getting_Started_with_gRPC_Go)
 - [Getting Started with gRPC-Go (Streaming)](codelabs/Getting_Started_with_gRPC_Go_Streaming)
+- [Getting Started with gRPC-Java](codelabs/Getting_Started_with_gRPC_Java)
+- [Getting Started with gRPC-Java (Streaming)](codelabs/Getting_Started_with_gRPC_Java_Streaming)
+- [Setup Basic gRPC OpenTelemetry Plugin in gRPC C++](codelabs/gRPC_Cpp_OpenTelemetry_Plugin)
+- [Setup Basic gRPC OpenTelemetry Plugin in gRPC-Python](codelabs/gRPC_Python_OpenTelemetry_Plugin)
 
 Please note that this list will keep updating as new codelabs are added to the
 repository. Make sure to check back regularly for new content!