Add docs for abstract class generators
Add docs for abstract class generators

Adds documentation for https://github.com/rails/rails/pull/39866

rafaelfranca/omg-rails,starknx/rails,rails/rails,MSP-Greg/rails,lcreid/rails,Envek/rails,Vasfed/rails,betesh/rails,kmcphillips/rails,Vasfed/rails,kddeisz/rails,Vasfed/rails,tjschuck/rails,vipulnsward/rails,kddeisz/rails,eileencodes/rails,esparta/rails,Erol/rails,yahonda/rails,rafaelfranca/omg-rails,rails/rails,rails/rails,esparta/rails,bogdanvlviv/rails,georgeclaghorn/rails,yalab/rails,tgxworld/rails,repinel/rails,yawboakye/rails,tgxworld/rails,MSP-Greg/rails,yahonda/rails,vipulnsward/rails,MSP-Greg/rails,bogdanvlviv/rails,schuetzm/rails,kmcphillips/rails,EmmaB/rails-1,yalab/rails,Erol/rails,betesh/rails,kddeisz/rails,yahonda/rails,yahonda/rails,EmmaB/rails-1,georgeclaghorn/rails,Erol/rails,BlakeWilliams/rails,tgxworld/rails,EmmaB/rails-1,Stellenticket/rails,repinel/rails,BlakeWilliams/rails,betesh/rails,Stellenticket/rails,kddeisz/rails,Vasfed/rails,bogdanvlviv/rails,tjschuck/rails,Edouard-chin/rails,georgeclaghorn/rails,BlakeWilliams/rails,joonyou/rails,schuetzm/rails,tjschuck/rails,esparta/rails,eileencodes/rails,joonyou/rails,joonyou/rails,yalab/rails,joonyou/rails,MSP-Greg/rails,tgxworld/rails,bogdanvlviv/rails,Edouard-chin/rails,Stellenticket/rails,lcreid/rails,yawboakye/rails,BlakeWilliams/rails,repinel/rails,Edouard-chin/rails,rafaelfranca/omg-rails,Envek/rails,yawboakye/rails,Edouard-chin/rails,rails/rails,Envek/rails,eileencodes/rails,esparta/rails,Erol/rails,starknx/rails,Stellenticket/rails,lcreid/rails,kmcphillips/rails,eileencodes/rails,schuetzm/rails,yawboakye/rails,tjschuck/rails,repinel/rails,georgeclaghorn/rails,kmcphillips/rails,schuetzm/rails,betesh/rails,Envek/rails,vipulnsward/rails,vipulnsward/rails,yalab/rails,lcreid/rails,starknx/rails