improved error wording
improved error wording

Fixed a grammatical mistake and made the meaning clearer by replacing "it" with "this" and by adding an example.

It does increase the length of the output, but I think it's much easier to read and more informative.
dkuku/platformio,platformio/platformio-core,mcanthony/platformio,platformio/platformio-core,valeros/platformio,mplewis/platformio,platformio/platformio,eiginn/platformio,atyenoria/platformio,mseroczynski/platformio,ZachMassia/platformio