Broken links in Project-Lifecycle.md

[williamkapke]

There is a broken "Proposal" under the Lifecycle section:
https://github.com/nodejs/TSC/blob/master/Project-Lifecycle.md#lifecycle

[williamkapke]

Also the "mentors" link under "Incubation" points to:
https://github.com/nodejs/TSC/blob/master/README.md#mentors

...which doesn't exist

EDIT:
Also the "DCO" link under "Applying To Join":
https://github.com/nodejs/TSC/blob/master/Project-Lifecycle.md#applying-to-join

[mikeal]

We should remove "apply to join" while the TSC isn't accepting applications.

[jasnell]

@williamkapke ... if this is still an issue, please reopen