http-plugin: Expand README.md

[JoshPaulie]

The following might also be added, but figured I'd propose the distilled version

/stats

Responds with the player's current stats

Example response (truncated)

[
  {
    "stat": "Attack",
    "level": 99,
    "boostedLevel": 99,
    "xp": 13047305
  },
  {
    "stat": "Defence",
    "level": 87,
    "boostedLevel": 87,
    "xp": 4004182
  }
]

/inv

Responds with the player's current inventory

Example response (truncated)

[
  {
    "id": 24691,
    "quantity": 1
  },
  {
    "id": 24691,
    "quantity": 1
  }
]

/equip

Responds with the player's current equipped items

Example response (truncated)

[
  {
    "id": 10941,
    "quantity": 1
  },
  {
    "id": 28136,
    "quantity": 1
  }
]