Add support of alternative README filenames for locales (ex: LISMOI in french)

Problem to solve

When setting up a french instance, I would like to have everything in French. But the README file can only be called README, I would like to call it "LISMOI" because it's french.

Further details

(Include use cases, benefits, and/or goals)

Proposal

Two possible solutions:

• per-project configuration to allow each user to setup which file to display by default
• per-instance configuration to allow to setup a rule for which file to display first (LISMOI > README.md > README)

What does success look like, and how can we measure that?

People who do not speak english may enjoy more using Gitlab. We can measure the number of projects using this configuration option.

(If no way to measure success, link to an issue that will implement a way to measure this)

Links / references

Example of somebody using this convention: https://github.com/tla/cpanmods/blob/master/Flemmv31/LISMOI.txt