Add Explanation of why Timeout is Doubled.

[PraddyumnYadav]

Added Explanation for why Timeout is Doubled.

• In this Pull Request I have Tried to Solve Connection timeout (not Read, Wall or Total) is consistently taking twice as long #5773 .

./docs/user/advanced.rst

+ **You need to be careful when using the timeout argument.**
+ If the specified domain has multiple IP addresses, `urllib3`_ will continue to try another IP address when the specified connection timeout is reached. Also, the connection timeout is applied for each attempt.
+ Requests are affected by this because you are using `urllib3`_.
+ This phenomenon can wait longer than you expect. Maybe it's the time that doubled the connection timeout.
+ Of course there may be more.
+ You can also consider extreme solutions, such as having the specified domain name return only one IP address.
+ For example, if DNS returns both IPv4 DNS records (A) and IPv6 DNS records (AAAA), patch it so that it does not return IPv6.
+ However, new issues may arise.

If it Suits Your Needs Consider Merging this Pull Request.

[sigmavirus24]

Fixed by #6600