Adding timeline explanation

DocumentStatus.md

@@ -1,5 +1,12 @@
 The following tables lists final and current documents produced by the File Format group of MPEG. Final documents are published by ISO, most of the time for a fee and sometimes free-of-charge (e.g. ISOBMFF used to be free of charge but is no longer unfortunately). MPEG Documents are usually internal documents only available to MPEG members, but some of them are public (e.g. working drafts, technologies under considerations, defect reports, etc.) and on [MPEG’s public site](https://www.mpeg.org/). The tables provide some links that are only accessible to MPEG members, and some that are public.
 
+In order to understand the table below, it may be useful to understand the timeline of a File Format standard, as follows:
+* Contributions proposing new technologies are submitted by companies and evaluated by the group. They are either noted, or accepted. If accepted and there is a consensus, the technology is added to a Working Draft (WD). If the technology is interesting but has not reached a consensus yet, it goes into a document called Defect Report or Technologies Under Considerations (TuC) to get improved. It can move from TuC or Defect Report to the WD when a consensus is reached.
+* When decided by the group, usually after 3 months, the WD is converted to a Committee Draft (CD). This triggers an official ballot that lasts 2 months (for amendments) or 3 months (for new standard).
+* When all the comments on the CD ballot are received and processed, a DAM or DIS is produced. This triggers a second official ballot that lasts 5-6 months.
+* When all the comments on the DAM/DIS ballot are received and processed, a FDAM/FDIS is produced. At this stage, the technology is frozen. This triggers a third ballot that lasts usually 2 months.
+* When all FDAM/FDIS (editorial) comments are received and processed, the document is delivered to ISO/IEC for publication. This can take several months (but sometimes several years!).
+
 ### 14496-12 | ISOBMFF 
 | Document Title | Link to latest public document (if any)                                                                           | MPEG output date | MPEG output number (MPEG-Member only)                                                                                                                                           | ISO status<br>(public page and editor-only)                                                                                                    | Description                                                                                                           |
 | ---------------------|-------------------------------------------------------------------------- | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------ |