Replace links to the `Merge request description format` section with
up-to-date instructions on using the MR template built into the UI.

The `Merge request description format` section was removed in 2f7e28d1,
but links were left in the table of contents and in the MR description
instructions.

All this does is convert the version sections into headers. The list
items shouldn't really be indented by two spaces, but it makes no
difference to the rendering and this way we retain authorship history
for the actual changes.

Related to https://gitlab.com/gitlab-org/release-tools/merge_requests/29

Signed-off-by: Rémy Coutable <remy@rymai.me>

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Signed-off-by: Rémy Coutable <remy@rymai.me>

Change to use a better title style

Add backticks to code segments

Spelling and Grammar

Adjust bug template to adhere to standard bug report format

* https://developer.mozilla.org/en-US/docs/Mozilla/QA/Bug_writing_guidelines
* Guidelines use the following format

- Summary
- Steps to Reproduce
- Expected Behaviour
- Actual Behaviour

These guidelines cover the performance requirement for newly submitted
merge requests. These guidelines are put in to place to prevent merge
requests from negatively impacting GitLab performance as much as
possible.

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gitlab-org/gitlab-ce/issues/14905#note_12235996

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Signed-off-by: Rémy Coutable <remy@rymai.me>

Now that we autoscale runner, we don't need to optimize for their usage
anymore. Abusing of "ci skip", for instance for view changes can lead to
broken specs, so let's just not use it!

Signed-off-by: Rémy Coutable <remy@rymai.me>

I noticed that the contributing guidelines still link to the thoughtbot
code review guidelines even though we already have our own.

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Add SCSS Lint, CSSComb config file, run SCSS Lint in GitLab CI, add documentation for SCSS Style Guide.

See !3069 for more information.

Also, link to this new paragraph in PROCESS.md and improved a bit this
document.

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Fixes #12784

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