use nix-shell to build on nixos

Fix #616. Add brief documentation for how to use it.

fix minor typo in doc template

Revert "Update snap installation instructions"

This reverts commit 5fd7bf7e61.

Apparently it is not just no longer necessary to use classic
confinement, but actually impossible, i.e. snap emits an error that the
zola snap is not compatible with `--classic`.

Fix format mistake

Add "Hello, Rust!" website to examples file

Correct a typo in the theme documentation

Add matthias-endler.de to list of examples

Remove redundant "From Source" documentation

0.5.1

Mark required Rust version as 1.29

690b3f9 updated the required version in Cargo.lock and in the CI config files, but not in the installation instructions.

add rendering for 404.html when running zola serve

Fixed name in Image Processing page

Add home plug to snapcraft.yml

This should fix permissions errors when initializing or writing files.

Fix typo

Closes #537

Update brew docs

Closes #521

Closes #533

Update snap installation instructions

If you don't install with classic confinement, you'll get permission errors trying to create sites with `zola init`.

Add instructions on how to deploy to GitLab pages