message: docs(README): uninstall instructions for debian/brew
  We have inline instructions to install Etcher from package managers.
  This commit extends them to quickly mention how to uninstall as well.
  Fixes:
diff: @@ -58,6 +58,14 @@ installers for all supported operating systems.
  sudo apt-get install etcher-electron
  ```
  +##### Uninstall
  +
  +```sh
  +sudo apt-get remove etcher-electron
  +sudo rm /etc/apt/sources.list.d/etcher.list
  +sudo apt-get update
  +```
  +
  #### Brew Cask (macOS)
  Note that the Etcher Cask has to be updated manually to point to new versions,
  @@ -68,6 +76,12 @@ release.
  brew cask install etcher
  ```
  +##### Uninstall
  +
  +```sh
  +brew cask uninstall etcher
  +```
  +
  Support
  -------
  