Readme fixes

[filipfranek88]

Hey, nice handy script. Thanks for that. As I went through the README, I encountered a few things I wanted to point out.

# add
cd shellgpt
# before
sudo cp ./chatgpt.sh /usr/bin/chatgpt
# and fix the typo in 
cp ./chatgpt ~/.chatgtp/  # where it should be
cp ./chatgpt ~/.chatgpt/

Also I was missing information about the BEARER, so I would add: "BEARER expects your API Token that you can create at https://beta.openai.com/account/api-keys"

[kpatronas]

Hi! thank you for the issue you spotted, i will fix them