Are questions about flowcharts appropriate on Software Engineering?
Questions about flow charts in general are not on topic here. We can't tell you whether your flow chart is correct, and we won't review or rate your flow chart. We can't help with using any drawing tool.
However, flow charts or activity diagrams are used as a documentation tool. Process-level questions on how diagrams fit into the system development life cycle (SDLC) are perfectly on topic and are welcome.
To a certain degree, concrete questions regarding problems with drawing a flow chart might be accepted by the community, e.g. if you are trying to express a flow as an activity diagram conforming to the UML 2.0 standard and are unsure how a certain scenario involving parallelism should be expressed. Precedent for such questions:
Assumed your flowchart is showing a high-level design of a piece of software, asking for reviewing the design can be on topic, as long as the question is clearly focused on some aspects of the design, and not just asking for a broad discussion.