Update Monster Statistics with size component from SRD 5.1 Monsters page

[DrFretNot]

Page 254 of the most recent SRD under the Creative Commons License includes the section on "Size" for Monsters that I have added.

Sources:

• https://www.dndbeyond.com/posts/1439-ogl-1-0a-creative-commons
• https://www.dndbeyond.com/attachments/39j2li89/SRD5.1-CCBY4.0License.pdf#page=254

[OldManUmby]

Sorry, this took sooo long to merge :). Done.