fix: update docs for cm account resource

[benbuchanan]

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Output from acceptance testing:

TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v -run TestAccIBMCmAccountBasic -timeout 700m 
=== RUN   TestAccIBMCmAccountBasic
--- PASS: TestAccIBMCmAccountBasic (13.88s)

TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v -run TestAccIBMCmAccountDataSourceBasic -timeout 700m 
=== RUN   TestAccIBMCmAccountDataSourceBasic
--- PASS: TestAccIBMCmAccountDataSourceBasic (12.11s)

[benbuchanan]

cc @hkantare