research the limitations of LINE Bot

[thewro11]

As the meeting from #9, we need to clarify this problem on the next meeting.

Acceptance Criteria:

• Research on what the limitation of free privilege of the LINE Bot is (e.g. request limit before throwing out the 429 timed-out status message, etc.).

[thewro11]

LINE Developer documentation specified the limit of message that can be sent to the user. It is written that the bot can reply to user's message at the maximum of 2,000 requests per second.