Merge branch 'mr-performance-guides' into 'master'

Added performance guidelines for new MRs

## What does this MR do?

This MR adds a set of guides that should be followed by merge request authors.

## Are there points in the code the reviewer needs to double check?

Spelling, grammar, etc

## Why was this MR needed?

There is no set of guidelines one should follow when submitting merge requests. This leads to developers at times disregarding performance. This in turn results in performance specialists having to clean up the mess, or production engineers being woken up in the middle of the night because the database is on fire.

## Does this MR meet the acceptance criteria?

- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

cc @DouweM @rspeicher @pcarranza @dzaporozhets 

See merge request !5905

1 files changed, 2 insertions, 0 deletions

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index c457af2ae6f..c77dcd96a7d 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -287,6 +287,8 @@ request is as follows:
    migrations on a fresh database before the MR is reviewed. If the review leads
    to large changes in the MR, do this again once the review is complete.
 1. For more complex migrations, write tests.
+1. Merge requests **must** adhere to the [merge request performance
+   guidelines](doc/development/merge_request_performance_guidelines.md).
 
 The **official merge window** is in the beginning of the month from the 1st to
 the 7th day of the month. This is the best time to submit an MR and get