[readme] Update shell profile file install notes

* Adds a note for how to fix the issue when the install script is not   updating the correct profile file.

Author: asadakbar

README.md

@@ -109,7 +109,7 @@ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.1/install.sh | bash
 wget -qO- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.1/install.sh | bash
 ```
 
-Running either of the above commands downloads a script and runs it. The script clones the nvm repository to `~/.nvm`, and attempts to add the source lines from the snippet below to the correct profile file (`~/.bash_profile`, `~/.zshrc`, `~/.profile`, or `~/.bashrc`).
+Running either of the above commands downloads a script and runs it. The script clones the nvm repository to `~/.nvm`, and attempts to add the source lines from the snippet below to the correct profile file (`~/.bashrc`, `~/.bash_profile`, `~/.zshrc`, or `~/.profile`). If you find the install script is updating the wrong profile file, set the `$PROFILE` env var to the profile file’s path, and then rerun the installation script.
 
 <a id="profile_snippet"></a>
 ```sh