Add "review period explanation" to README

[balotofi]

as the procedures and reports would be most beneficial for project managers that may want to use BIRDS resources,
research the main points of review in a satellite project

• PDR
• MDR
• CDR
  briefly explain these points, visual aids like diagrams (schedule, concise gantt chart) may be helpful, to help new program managers understand where the files in this repo would be most helpful