Update captions.py

[amspsingh04]

i have added a function generate_txt_captions which can be used to generate a text file from the srt file of captions that is generated before this

an example of its working on my device (this is just a 10 sec chunk of the 1min video, it worked perfectly for the entire length, and for another 10 videos as well of 30 min + length, would be happy to share another working example if needed)

video url - https://www.youtube.com/watch?v=MpcQOSE3vM4
srt content generated:

1
00:00:00,420 --> 00:00:05,220
hello everybody

2
00:00:02,700 --> 00:00:07,020
welcome to a demo video of my real-time

3
00:00:05,220 --> 00:00:10,139
transcription library that should

txt content generated:
hello everybody welcome to a demo video of my real-time transcription library that should

i am not well versed with parsing and using XML content, that is why i have used regex on the srt output.