DOC: Better naming of the part.

"ITK Community Participation" to me is more of a social
term that might better describing the community health
and community building ( includng the statistics on gerrit, git,
and  mailinglist etc).

I propose to use "Development Guidelines" instead.

Change-Id: I3d176db8dc366555e5d8d2235f725f5ea3752bf7
Merge "DOC: Better naming of the part."