Add more repo topics so CumulusCI is easier to find

[Julian Joseph]

Describe the solution you'd like

Example list of topics pulled from https://github.com/hardisgroupcom/sfdx-hardis that may be a good starting place:

plugin documentation devops quality automation deployment organization salesforce apex salesforce-lightning scratch code-quality cicd salesforce-metadata salesforce-developers salesforce-api salesforcedx sfdx data-loader salesforce-apex