Added timedelta feature and timezone conversion

[bakayu]

closes #1 closes #2 closes #3

[dubesar]

Hi @bakayu, please update the testing done as well in the details.

[bakayu]

Updated as per your feedback :)

testing:

timedelta and usage of short timezone codes

worldtimebuddy --timezone IST --delta +2hr
Asia/Kolkata                   2024-10-07 01:40:07

worldtimebuddy --timezone JST --delta +5day
Asia/Tokyo                     2024-10-12 03:10:11

worldtimebuddy --timezone UTC --delta -1min
UTC                            2024-10-06 18:09:13

[bakayu]

Updated as per your feedback :)

additional testing:

worldtimebuddy --timezone UTC --delta +2
DeltaValueError: Invalid time format. Use +2hr, -30min, -1day, etc.

worldtimebuddy --timezone IST --delta -1day
Asia/Kolkata                   2024-10-06 00:26:31

worldtimebuddy --timezone IST --delta -1hr
Asia/Kolkata                   2024-10-06 23:26:35

[bakayu]

I have updated the README.md file to include delta function use cases and added an insallation guide as well this closes #3 as well now

[dubesar]

LGTM, will approve and merge after one more round of review!

[bakayu]

updated README.md file

[bakayu]

please review.

[dubesar]

Merged!

[bakayu]

please add the hacktoberfest-accepted label, thanks! ^^