docs: Tidies initial help page

Description

Polishes the punctuation, phrasing, capitalization, and spelling of the initial help page.

Text output before

ENVIRONMENT VARIABLES
  GITLAB_TOKEN: an authentication token for API requests. Setting this avoids being
  prompted to authenticate and overrides any previously stored credentials.
  Can be set in the config with 'glab config set token xxxxxx'

  GITLAB_HOST or GL_HOST: specify the url of the gitlab server if self hosted (eg: https://gitlab.example.com). Default is https://gitlab.com.

  REMOTE_ALIAS or GIT_REMOTE_URL_VAR: git remote variable or alias that contains the gitlab url.
  Can be set in the config with 'glab config set remote_alias origin'

  VISUAL, EDITOR (in order of precedence): the editor tool to use for authoring text.
  Can be set in the config with 'glab config set editor vim'

  BROWSER: the web browser to use for opening links.
  Can be set in the config with 'glab config set browser mybrowser'

  GLAMOUR_STYLE: environment variable to set your desired markdown renderer style
  Available options are (dark|light|notty) or set a custom style
  https://github.com/charmbracelet/glamour#styles

  NO_PROMPT: set to 1 (true) or 0 (false) to disable and enable prompts respectively

  NO_COLOR: set to any value to avoid printing ANSI escape sequences for color output.

  FORCE_HYPERLINKS: set to 1 to force hyperlinks to be output, even when not outputing to a TTY

  GLAB_CONFIG_DIR: set to a directory path to override the global configuration location

LEARN MORE
  Use 'glab <command> <subcommand> --help' for more information about a command.

FEEDBACK
  Encountered a bug or want to suggest a feature?
  Open an issue using 'glab issue create -R gitlab-org/cli'

Text output after

ENVIRONMENT VARIABLES
  GITLAB_TOKEN: An authentication token for API requests. Set this variable to
  avoid prompts to authenticate. Overrides any previously-stored credentials.
  Can be set in the config with 'glab config set token xxxxxx'.

  GITLAB_HOST or GL_HOST: Specify the URL of the GitLab server if self-managed.
  (Example: https://gitlab.example.com) Defaults to https://gitlab.com.

  REMOTE_ALIAS or GIT_REMOTE_URL_VAR: A 'git remote' variable or alias that contains
  the GitLab URL. Can be set in the config with 'glab config set remote_alias origin'.

  VISUAL, EDITOR (in order of precedence): The editor tool to use for authoring text.
  Can be set in the config with 'glab config set editor vim'.

  BROWSER: The web browser to use for opening links.
  Can be set in the config with 'glab config set browser mybrowser'.

  GLAMOUR_STYLE: The environment variable to set your desired Markdown renderer style.
  Available options: dark, light, notty. To set a custom style, read
  https://github.com/charmbracelet/glamour#styles

  NO_PROMPT: Set to 1 (true) or 0 (false) to disable or enable prompts.

  NO_COLOR: Set to any value to avoid printing ANSI escape sequences for color output.

  FORCE_HYPERLINKS: Set to 1 to force hyperlinks in output, even when not outputting to a TTY.

  GLAB_CONFIG_DIR: Set to a directory path to override the global configuration location.

Related Issues

Resolves #[issue_number]

How has this been tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)