doc: add @shigeki and @mscdex to TC

voted in to Node.js Foundation TSC in meeting on 2015-06-17

Closes: https://github.com/nodejs/io.js/issues/1500
Closes: https://github.com/nodejs/io.js/issues/1501
PR-URL: https://github.com/nodejs/io.js/pull/2008


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>