Document twistcli configurable vars for CI scan jobs

[iansk]

Question from the field:

Is this field only used for build number from Jenkins? We'd like to be able to pass in an arbitrary value for non-Jenkins setups… one use case is the Github URL to the build. Is this possible?

Answer from Michael:

set the BUILD_ID environment variable to populate this.

the JOB_NAME env var will populate the project field

Other two env vars picked up by twistcli: GIT_BRANCH and NODE_NAME