docs: invalid example, vim docs are outdated?

[tmillr]

See #340

There is an example in the vim docs which doesn't work, and has multiple issues. It doesn't appear in the README, but it is found in Usage.md as well. It should probably just be removed since the same behavior can be achieved in/via setup()?

Overrides

The individual components, such as [palettes][palette], [specs][spec], and [groups][group], can be overridden separately to customize the theme according to your preferences.

local override = require('github-theme').override
override.palettes({
  github_dark = {
    red = '#ff0000',
  },
  github_light = {
    comment = '#636e7b',
  },
})
override.specs({
  github_dark = {
    syntax = {
      keyword = 'magenta'
    }
  }
})
override.groups({
  all = {
    IncSearch = { bg = 'palette.cyan' },
  },
})

Issues with the example:

1. .overrides at the top should be apart of the require string/path
2. overrides.{specs,palettes,groups} lower in the example are not functions (and shouldn't be called)
3. Doing overrides this way may be sensitive to whether it's done before or after calling setup() and/or loading the theme (with :colorscheme ...)

[tmillr]

Fixed in a24960a