doc: backport reduce-memory.md from 1.21-dev
doc: backport reduce-memory.md from 1.21-dev

Changes:
- bitcoin -> dogecoin
- 0.14.0 -> 1.14.0

patricklodder/dogecoin,dogecoin/dogecoin,patricklodder/dogecoin,dogecoin/dogecoin,dogecoin/dogecoin,patricklodder/dogecoin,dogecoin/dogecoin,patricklodder/dogecoin,dogecoin/dogecoin,patricklodder/dogecoin,dogecoin/dogecoin