Add baseline Profiler documentation

[CAM-Gerlach]

Issue Description

Currently, all the main Spyder panes have at least a short page of documentation dedicated to them (with the outline covered in the Editor's doc, and the breakpoints pane discussed in Debugging)—except for the profiler, a much more significant feature than many of these. Therefore, we should include at least a stub length doc similar to the others (e.g. static analysis) for completeness. This would be done after I actually push the PR for #13 , and then after I'd merge the former I'd rebase and add the profiler links to the appropriate places in the other docs.