doc: improvements to child_process, process docs

Sort links in lexical order. Add missing links.
Add `disconnect` event description in Process doc.
Fix typos.

R-URL: #5075
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Robert Jefe Lindstädt <[email protected]>
Reviewed-By: Roman Reiss <[email protected]>

Author: estliberitas