Documentation work for SDHI SMS v3.1.2

[sumghai]

Imgur

• Update brochure images of exploded views
• Update brochure images of example mission

General

• Update release notes in SDHI_SMS_README.txt

KSP Forums

• Update release thread OP

CurseForge

• Update thumbnail for CurseForge
• Update gallery
• Update description

GitHub

• Update SDHI SMS stack assembly instructions on wiki with new screenshots and notes on the new fairing panels
• Update release notes
• Update README.md