Add Usage section in readme for submodules

[dishankkalra23]

Please add usage section for submodules in this repository. Please refer the usage section in CBR module: https://github.com/terraform-ibm-modules/terraform-ibm-cbr/tree/main/modules/cbr-zone-module#usage

[ocofaigh]

@dishankkalra23 There is a usage - are you saying its not correct? https://github.com/terraform-ibm-modules/terraform-ibm-external-secrets-operator?tab=readme-ov-file#usage

[dishankkalra23]

I meant the usage section in submodules' readme is not present.

[vbontempi]

opened PR #181