Update README.md with the nvm, yarn setup steps (opensearch-project#317)

This commit adds the installation steps of yarn and npm
in the README.md file before the setup.

Signed-off-by: Venu Vardhan Reddy Tekula <venu@bitergia.com>

README.md

@@ -42,6 +42,8 @@ Or
 * After extracting, run ```bin/opensearch``` inside of the extracted build artifact dir
 
 To run Dashboards with OpenSearch
+* [Yarn](https://classic.yarnpkg.com/en/docs/install) is required for building and running the OpenSearch Dashboards
+* Install [nvm](https://github.com/nvm-sh/nvm/blob/master/README.md) to use the Node 10.23.1 version as it is required
 * Run ```yarn osd bootstrap``` in the OpenSearch Dashboards directory
 * While OpenSearch is running locally, run ```yarn start```
 * You can now navigate to ```http://localhost:5603``` where Dashboards runs by default