wireshark: update README instructions
wireshark: update README instructions

Minor tweaks to the README to make the email suggestion follow the format
used in other meta-openembedded README files and adding clarification on
building wireshark in a GUI environment.

Acked-by: Armin Kuster <65ab3e867b262c6052b2aaec32dae97b24ac0759@mvista.com>
Signed-off-by: Joe MacDonald <fbe30f12b401d02c5cf3f5c053fced92c546e3de@mentor.com>

WindRiver-OpenSourceLabs/meta-networking