[DATA] Add missing Monster descriptions to SRD 5.1 Miscellaneous Creatures

[calumbell]

Bug description

Descriptive text for monsters listed in the WotC SRD 5.1 is generally omitted, with the notable exception of the Miscellaneous Creatures section (Appendix MM-A, starting pp. 366).

Note that the Awakened Shrub and Awakened Tree include a brief description following the statblock. This should be added to the relevant API entry's "desc" field