GitLab

This drops many entries from the menu, as they would break when using
Gedit on a phone.

This helps it fit into phone screens.

This avoids presenting it to regular users as it doesn't fit phone
screens, while allowing advanced users to enable it back.

This will help it fit in phone screens.

New news format, to follow the same format as GtkSourceView, gspell,
Tepl, and other projects. Adding the date is convenient, instead of
looking in the git log.

I'm now motivated again by being a gedit maintainer.

There is a lot of possible work to do in gedit. gedit was unmaintained
recently, then a few developers have helped, including Jeremy Bicha for
the releases. But I think more co-maintainers is always welcome.

The task structure can be improved over time, but it shouldn't be too
strict with lots of fields.

Maybe there is a best-practice for writing roadmaps, like
[semver](https://semver.org/) for version numbers?

Signed-off-by: Trần Ngọc Quân <vnwildman@gmail.com>

The James Henstridge Build. And James has contributed recently to
gedit :-) ! So I will spell his old project correctly.

I have the intention to add:
- build-with-jhbuild.md

"install-with-jhbuild.md" sounds a slightly less good name. Jhbuild is
usually used for contributors, and we talk more about "the build",
instead of "the installation".

It's supported by both GitLab and GitHub.

The content from the Build section of
gedit-development-getting-started.md is moved to install.md.

And write many more explanations.

It's a first step to put all the build/install instructions in a single
place (there are also explanations in
docs/gedit-development-getting-started.md that will be moved in a
following commit).

The file is now fully in Markdown.

Add a link to the GtkSourceView HACKING file, and don't duplicate its
content in the gedit CONTRIBUTING file. It's a big simplification. In
the past I've synced the two files between GSV and gedit, then I've
improved the GSV HACKING file but I was no longer contributing to gedit
so the gedit file was not updated; now it's fixed.

The "Building from git" section is already explained in the
`docs/gedit-development-getting-started.md` file.

Inspired by the content from the old gedit website:
https://projects-old.gnome.org/gedit/developers.html

I intend to add a section "Contributions other than software
development" with links to wiki pages.

The term "hacking" is for software development only, so it's less
appropriate.

A next commit will rename the file to CONTRIBUTING.md (with the
extension), and use the Markdown syntax.