Add LGTM code quality badges

[xcorail]

Hi there!

I thought you might be interested in adding these code quality badges to your project. They will indicate a very high code quality to potential users and contributors.
To get an idea of the analyses reflected by these grades, check the alerts discovered by LGTM.

N.B.: I am on the team behind LGTM.com, I'd appreciate your feedback on this initiative, whether you're interested or not, if you find time to drop me a line. Thanks.

[garethahealy]

Looks nice and very similar to sonarcloud, but how are the stats updated? do you guys have a cronjob running watching the repo? or do i need to manually run something?

[xcorail]

Hey @garethahealy

No need for a manual intervention

• We are polling the repos once a day, and analysed all new commits, most recent first
• But our recommended usage is to integrate PR integration. LGTM will report any new problem (or fix) directly within the PR, and it's immediate, not once a day. It's a one-click operation, you can easily give it a try and let me know