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[ymd-h]

In order to make tf2rl more friendly, I suggest updating of README and Reference Site.

• [x] Add Numbering at headings (#153)
• [x] Make clearer that there are several ways of installation (#153)
• [x] Add Usage section (#153)
• [ ] Available option for each algorithm
  • [x] DQN (#156, #157)
  • [x] DDPG (#156, #157)
  • [x] CategoricalDQN (#157)
  • [x] TD3 (#157)
  • [x] BiResDDPG (#157)
  • [x] VPG (#157)
  • [x] PPO (#157)
  • [x] SAC (#157)
  • [x] SAC+AE (#158)
  • [x] CURL (#158)
  • [x] GAIL (#158)
  • [x] GAIfO (#158)
  • [x] VAIL (#158)
  • [x] Trainer (#158)
  • [x] MPC Trainer (#158)
  • [x] ME-TRPO Trainer (#158)
  • [x] On Policy Trainer (#158)
  • [x] IRL Trainer (#158)
  • [ ] etc
• [ ] Difference between continuous/discrete algorithm usage (if exists)
• [ ] Ape-X and other special usage
• [ ] Write missing docstring for some classes
  • [x] DQN (#156, #157)
  • [x] DDPG (#156, #157)
  • [x] CategoricalDQN (#157)
  • [x] TD3 (#157)
  • [x] BiResDDPG (#157)
  • [x] VPG (#157)
  • [x] PPO (#157)
  • [x] SAC (#157)
  • [x] SAC+AE (#158)
  • [x] CURL (#158)
  • [x] GAIL (#158)
  • [x] GAIfO (#158)
  • [x] VAIL (#158)
  • [x] Trainer (#158)
  • [x] MPC Trainer (#158)
  • [x] ME-TRPO Trainer (#158)
  • [x] On Policy Trainer (#158)
  • [x] IRL Trainer (#158)
  • [ ] etc
• [ ] Describe detail at sphinx reference site
  • [x] Adjust config to show Google Style docstring (#156)
  • [ ] etc
• [ ] Type Hinting