Update resource_consul_cluster_root_token.go

[srikrishmurthy]

Changed the description
a) Existing text about invalidation is incorrect
b) Clarified that this token is similar to the one provided in the HCP Consul UI

🛠️ Description

🚢 Release Note

Release note for CHANGELOG:

* {affected resource | docs | all}: {Brief description of change} [GH-nnnn]

🏗️ Acceptance tests

• Are there any feature flags that are required to use this functionality?
• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccXXX'

...

[mkeeler]

LGTM