Remove Mention of Bitbucket in README

[blonienc]

The README still mentions Bitbucket as our repo source but are now fully using Github. We need to remove mention of this so those being onboarded are not misdirected.

[shrutitirpude]

The README looks good and does not point to bitbucket
The confluence page was pointing to the secureli repository in bitbucket, updated the confluence page with github repository link : https://slalom.atlassian.net/wiki/spaces/STFT/pages/2997126307/seCureLI

[shrutitirpude]

Updated the onboarding confluence page removing steps fot bitbucket and adding steps for github access : https://slalom.atlassian.net/wiki/spaces/STFT/pages/3003285586/Onboarding+Checklist
Updated the jira board link with github board link