Update plaintexteditprops.md

[gregpalaci]

adds plaintextedit example and link to qplaintextedit

[shubhamzanwar]

Thanks for working on docs to make things easier for users!
We are using typedoc for automatically generating docs. Instead of modifying the content in the .md files, you could add it as a comment in the component files itself.
Take a look at

react-nodegui/src/components/Button/RNButton.ts

Line 10 in f7b354d

* The Button component provides ability to add and manipulate native button widgets. It is based on

for example.

Happy to approve this PR if you could move the content to the appropriate component file! 😁

[gregpalaci]

aha ok will migrate to that format tomorrow, thanks!

[gregpalaci]

#291