Staging the changes in git

git status

git add -A stages all changes

git add . stages new files and modifications, without deletions

git add -u stages modifications and deletions, without new files

git add -A is equivalent to git add .; git add -u

git add -A is equivalent to git add --all

git add -u is equivalent to git add --update

References
https://stackoverflow.com/questions/572549/difference-between-git-add-a-and-git-add
https://git-scm.com/docs/git-stage
https://git-scm.com/docs/git-add

Signing commits in git

gpg --list-secret-keys --keyid-format LONG

From the list of GPG keys, copy the GPG key ID you’d like to use. In this example, the GPG key ID is 3AA5C34371567BD2

$ gpg --list-secret-keys --keyid-format LONG
/Users/hubot/.gnupg/secring.gpg
------------------------------------
sec   4096R/3AA5C34371567BD2 2016-03-10 [expires: 2017-03-10]
uid                          Hubot 
ssb   4096R/42B317FD4BA89E7A 2016-03-10
git config --global user.signingkey 3AA5C34371567BD2

or

git commit -S -m your commit message

References
https://help.github.com/en/articles/telling-git-about-your-signing-key
https://git-scm.com/book/en/v2/Git-Tools-Signing-Your-Work
https://help.github.com/en/articles/signing-commits

Migrate from Bitbucket to GitHub

Check out the existing repository from Bitbucket

git clone https://USER@bitbucket.org/USER/PROJECT.git

Add the new Github repository as upstream remote of the repository checked out from Bitbucket

cd PROJECT
git remote add upstream https://github.com:USER/PROJECT.git

Push all branches

git push upstream master
git push --tags upstream

References
https://medium.com/@RobertKhou/how-to-migrate-from-bitbucket-to-github-75c87a892767