doc: add SECURITY_WG_GITHUB_TOKEN request

[RafaelGSS]

Refs: #949

permissions on [`nodejs/security-wg`](http://github.com/nodejs/security-wg):
  contents: write
  pull-requests: write

[aduh95]

To whoever who lands this: careful, the token should be saved on the nodejs-private/security-release, not on the public repo – I mean, I guess we can save it on the public repo as well, but currently it's not necessary. @RafaelGSS am I understanding things correctly?

Side node: maybe the current table is not well fitted for this kind of "cross-repo tokens". /cc @legendecas

[RafaelGSS]

To whoever who lands this: careful, the token should be saved on the nodejs-private/security-release, not on the public repo – I mean, I guess we can save it on the public repo as well, but currently it's not necessary. @RafaelGSS am I understanding things correctly?

Side node: maybe the current table is not well fitted for this kind of "cross-repo tokens". /cc @legendecas

Correct

[legendecas]

Side node: maybe the current table is not well fitted for this kind of "cross-repo tokens".

For additional repo permissions, we can list the request in the PR description. The table should list where the token is installed, so that we can rotate the token by the table.

[mhdawson]

LGTM

[mhdawson]

I believe I've added the token as requested