Add documentation for the --rerun option

The --rerun option brought over from HSC was lacking good
documentation. This ticket provides said documentation by sumamrizing
the relevent contents of RFC-95: Filesystem Organization & Argument
Parser Features.

doc/main.dox

@@ -119,6 +119,44 @@ Thus the following example specifies all sensors for four combinations of visit
 plus all sensors for one raft of two other visits for calibrated lsstSim data:
 - `--id visit=54123^55523 raft=1,1^2,1 --id visit=623459^293423 raft=0,0`
 
+\subsection pipeBase_argumentParser_rerun The --rerun Option
+
+The `--rerun` option is a convenient shortcut for specifying the output directory of a command line task and
+serves the same purpose as the `--output` argument. However, the value supplied to `--rerun` is relative to
+the "rerun" directory of the root input data repository (i.e. follow the "_parent" chain all the way back,
+then add "rerun" to that). `--rerun` saves the user from typing in the input repository twice. For example:
+
+`processCcd.py $root/hsc --output $root/hsc/rerun/vpk24/DM-4443`
+
+which will run processesCcd on the (HSC) data in "$root/hsc" and put the output in 
+"$root/hsc/rerun/vpk24/DM-4443" can be shortened by using `--rerun` to
+
+`processCcd.py $root/hsc ----rerun vpk24/DM-4443`
+
+This is useful because outputs from the pipeline usually go within the camera-level root repository into a
+subdirectory of a "rerun" directory present in the camera-level root repository. These output sub-directories
+should usually be named using JIRA issue numbers and dates, again with a distinction between public and
+private reruns. For example:
+
+`$root/hsc/rerun/DM-3456_20150607`   # a public rerun useful for many people
+
+`$root/hsc/rerun/jbosch/DM-7890/fixed-psf`   # one of several private reruns used to debug a single issue
+
+`$root/lsstSim/krughoff/DM-5678/rerun/jbosch/DM-5679`   # simulated by Simon, processed by Jim
+
+As with any other output repository, reruns can be chained, but keep in mind that the name of the parent rerun
+is not generally recorded in the name of the child. Chaining is made easy by supporting a two-value 
+form separated by a colon, which specifies both a parent rerun and the new output directory. For example:
+
+`processCcd.py $root/hsc --rerun price/DM-5680 ...`   # Paul processes some CCDs
+
+`makeCoaddTempExp.py $root/hsc --rerun price/DM-5680:jbosch/DM-5681 ...`   # Jim uses Paul's CCD processing to
+start a coadd.
+
+The `--rerun` can also specify a path, part of which can be a symbolic link. For example, if 
+"$root/hsc/rerun/rhl" -> "/other/disk/rhl/rerun", then `--rerun rhl/tmp/foo` creates "/other/disk/rhl/tmp/foo"
+where note that if the path is absolute, it is taken to be the path.
+
 \subsection pipeBase_argumentParser_argumentFiles Argument Files
 
 You may specify long or repetitive command-line arguments in text files and reference those files