Merge pull request #324352 from Aleksanaa/doc/meta

## Standard meta-attributes {#sec-standard-meta-attributes}

If the package is to be submitted to Nixpkgs, please check out the

[requirements for meta attributes](https://github.com/NixOS/nixpkgs/tree/master/pkgs#meta-attributes)

in the contributing documentation.

It is expected that each meta-attribute is one of the following:

### `description` {#var-meta-description}

A short (one-line) description of the package.

This is displayed on [search.nixos.org](https://search.nixos.org/packages).

Don’t include a period at the end. Don’t include newline characters. Capitalise the first character. For brevity, don’t repeat the name of package --- just describe what it does.

The general requirements of a description are:

- Be short, just one sentence.

- Be capitalized.

- Not start with definite ("The") or indefinite ("A"/"An") article.

- Not start with the package name.

  - More generally, it should not refer to the package name.

- Not end with a period (or any punctuation for that matter).

- Provide factual information.

  - Avoid subjective language.

Wrong: `"libpng is a library that allows you to decode PNG images."`

Right: `"A library for decoding PNG images"`

Right: `"Library for decoding PNG images"`

### `longDescription` {#var-meta-longDescription}