Merge pull request #131 from buildkite/SUP-2350-Matrix-Workflow-Jobs

SUP-2350 - Matrix and jobs via workflow docs note

Author: james2791

docs/CircleCI.md

@@ -89,5 +89,6 @@ The Buildkite Migration tool's currently supported (✅), partially supported (
 | `workflows.<name>.jobs.<name>.filters` | ✅ | The `branches` and `tag` filters that will determine the eligibility for a CircleCI to run. |
 | `workflows.<name>.jobs.<name>.filters.branches`| ✅ | The specific `branches` that are applicable to the `job`'s filter. Translated to a [step conditional](https://buildkite.com/docs/pipelines/conditionals#conditionals-in-steps). |
 | `workflows.<name>.jobs.<name>.filters.tags` | ✅ |  The specific `tags` that are applicable to the `job`'s filter. Translated to a [step conditional](https://buildkite.com/docs/pipelines/conditionals#conditionals-in-steps). |
+| `workflows.<name>.jobs.<name>.matrix` | ✅ | The `matrix` key allows running a specific job as part of a workload with different values. Translated to a [build matrix](https://buildkite.com/docs/pipelines/build-matrix) setup within a [command step](https://buildkite.com/docs/pipelines/command-step). |
 | `workflows.<name>.jobs.<name>.requires` | ✅ | A list of `jobs` that require this `job` to start. Translated to explicit [step dependencies](https://buildkite.com/docs/pipelines/dependencies#defining-explicit-dependencies) with the `depends_on` key. | 
 | `workflows.<name>.when` | ✅ | Conditionals that allow for running a workflow under certain conditions. The Buildkite Migration tool allows for the speicification using Logical operators `and`, `or` and `not` in creating command conditionals. |