Sort .gitignore.
doc workflow markdown style

- add h1 to README
- move h1 in workflow.md to h2 since the top image acts as h1
- typos
Merge pull request #8497 from cirosantilli/h1-workflow-readme

doc workflow markdown style
Merge pull request #7782 from cirosantilli/sort-gitignore

Sort .gitignore.
Allow a user to specify a channel and username for the slack-webhook