Remove the section related to webpacker installation

Author: ahangarha

README.md

@@ -787,30 +787,6 @@ You may see a warning like this when building a Webpack bundle using any version
 + module.exports = merge({}, webpackConfig, ignoreWarningsConfig)
 ```
 
-### During installation
-1) While using installers.(rails webpacker:install:react && rails webpacker:install)
-Error:
-```
-public/packs/manifest.json. Possible causes:
-1. You want to set webpacker.yml value of compile to true for your environment
-   unless you are using the `webpack -w` or the webpack-dev-server.
-2. webpack has not yet re-run to reflect updates.
-3. You have misconfigured Webpacker's config/webpacker.yml file.
-4. Your webpack configuration is not creating a manifest.
-or
-yarn: error: no such option: --dev
-ERROR: [Errno 2] No such file or directory: 'add'
-```
-Fix: Try updating yarn package.
-```
-sudo apt remove cmdtest
-sudo apt remove yarn
-curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
-echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
-sudo apt-get update && sudo apt-get install yarn
-
-yarn install
-```
 ### Undefined Set
 ```
 ExecJS::ProgramError (identifier 'Set' undefined):