Merging in the new documentation for custom types in Schematics.
Merging in the new documentation for custom types in Schematics.

Merge branch 'doc-base-type' of https://github.com/estebistec/schematics into doc_base_type

NerdWallet/schematics,kstrauser/schematics,eatfirst/schematics,ee08b397/schematics,kstrauser/schematics,openprocurement/schematics,promptworks/schematics,kaiix/schematics,not-napoleon/schematics,ee08b397/schematics,not-napoleon/schematics,mlyundin/schematics,promptworks/schematics