[Docs] remove note about "global install", since `nvm` is not intended for multiuser installs.

Per https://github.com/creationix/nvm/issues/918#issuecomment-161527422

README.markdown

@@ -25,7 +25,7 @@ or Wget:
 <sub>The script clones the nvm repository to `~/.nvm` and adds the source line to your profile (`~/.bash_profile`, `~/.zshrc` or `~/.profile`).</sub>
 
 You can customize the install source, directory and profile using the `NVM_SOURCE`, `NVM_DIR`, and `PROFILE` variables.
-Eg: `curl ... | NVM_DIR=/usr/local/nvm bash` for a global install.
+Eg: `curl ... | NVM_DIR="path/to/nvm" bash`
 
 <sub>*NB. The installer can use `git`, `curl`, or `wget` to download `nvm`, whatever is available.*</sub>