Adding Helium-SR1 Release Notes

Based on the wiki page here:
https://wiki.opendaylight.org/view/Simultaneous_Release:Helium-SR1_Combined_Release_Notes

Also fixes a typo in the section title "Known Issues and Limitation"
by pluralizing Limitations and fixes the link to known bugs to be for
all projects in OpenDaylight, not just the controller.

Change-Id: Ic15ec788c602f6619990b57c93cb959d3465ed30
Signed-off-by: Colin Dixon <colin@colindixon.com>