add blue color to README.md

[xBZZZZ]

blue color appears in papirus-folders -l but not in https://github.com/PapirusDevelopmentTeam/papirus-folders#preview

it's supposed to exist in README.md because it already exists in markdown code but github's markdown compiler ignores it https://github.com/PapirusDevelopmentTeam/papirus-folders/blob/b3319bf0d11e749c7e231778d73adf4a61eec894/README.md?plain=1#L19

this pull request shifts columns →↓ to not ignore blue color but creates 2 empty cells ↘ because odd number of colors

$ papirus-folders -l
List of available colors:

   adwaita
   black
 > blue
   bluegrey
   breeze
   brown
   carmine
   cyan
   darkcyan
   deeporange
   green
   grey
   indigo
   magenta
   nordic
   orange
   palebrown
   paleorange
   pink
   red
   teal
   violet
   white
   yaru
   yellow

[SmartFinn]

I didn't add the blue color in the list because this is the default folder color. But if you think it should be here - OK.

[xBZZZZ]

thank you for merge

I didn't add the blue color in the list because this is the default folder color.

sorry, I named this pull request badly

blue existed but in wrong place before this pull request

markdown source code looked like this:

| Name | Preview | Name | Preview |
|:-----|:-------:|:-----|:-------:|
| **adwaita** | img img img | **black** | img img img | **blue** | img img img |
| **bluegrey** | img img img | **breeze** | img img img |

(replaced !\[[^]]+]\([^)]+\) regexp with img for readability)

see how first non-header row has 6 columns (header and other rows have 4 columns)

[SmartFinn]

Oh, now I see. Thanks.