Fixed README with installation instructions for Docker and fixed MySQL errors due to SQLite default

[pUrGe12]

Proposed change

1. The issue with the current documentation is that it is not giving a complete explanation for how to install nettacker properly and run it. I have updated the README with the following changes:

• Code install docker-compose and docker (the user might face trouble with this if doing this for the first time, like I was)
• Changed the container name from nettacker-nettacker-1 to nettacker in the second command.
  This was because when I tried running it locally on a new machine, I got the following error:
  Error response from daemon: No such container: nettacker-nettacker-1
  Hence, the change.

2. Fixed MySQL errors fixing MySQL connections fail due to SQLite specific config in DbConfig #999 and MySQL not working #555

3. Corrected MySQL server name using pymysql.

4. Updated docstring for DbConfig class for MySQL related parameters

5. Corrected db.py file to include pymysql, change arguments based on engine name and improved remove_old_logs function with pymysql required changes.

Type of change

• New core framework functionality
• Bugfix (non-breaking change which fixes an issue)
• Code refactoring without any functionality changes
• New or existing module/payload change
• Localization improvement
• Dependency upgrade
• Documentation improvement

Checklist

• I've followed the [contributing guidelines][contributing-guidelines]
• I've run make pre-commit, it didn't generate any changes
• I've run make test, all tests passed locally

Additional comments:

1. The user needs to install pymysql using pip install pymysql
2. The user needs to ensure their server can handle multiple requests, they can do that using SET GLOBAL max_connections = 1000;
   [contributing-guidelines]: https://nettacker.readthedocs.io/en/latest/Developers/

[securestep9]

Hi @pUrGe12 Re: README changes - these are coming with a bigger documentation updates we are working on including re-vamped Dockerfile. Re: mySQL issues - it appears a misconfiguration and we are working on improving the documentation to make it clearer as well