docs: specify to use yarn v1 not v2 (#3799)

Co-authored-by: David Luzar <luzar.david@gmail.com>

.gitignore

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README.md

 #### Requirements
 
 - [Node.js](https://nodejs.org/en/)
-- [Yarn](https://yarnpkg.com/getting-started/install)
+- [Yarn](https://yarnpkg.com/getting-started/install) (v1 or v2.4.2+)
 - [Git](https://git-scm.com/downloads)
 
 #### Clone the repo