Add shortcuts to some improvements

[HaneulCheong]

• Added a missing hyphen to the first heading of README.md
• Changed four remaining global uniques to building uniques in Buildings.json (See b420936f004ef828e4b9fa75e3b62e7c531a0c5b)
• Added the following improvement-shortcut pairs:
  • Farm - F
  • Tree plantation - T
  • Mine - M
  • Pasture - P
  • Moisture trap - E
  • Solar collector - L
  • Wind farm - W
  • Research site - H
  • Hacking site - H
  • Salvage site - S
  • Water pump - W
  • Camp - C
  • Oil well - W
  • Energy farm - Y
  • Fort - O
  • Road, Railroad - R
  • Remove X - X
  • Cancel improvement order - .