Make install needs Sudo #417

When we installed this using Homebrew, the warning of the same name as core formulae occurred.
Hence, make install is essential for us.
However, this process needs to run with sudo.
Therefore, the correct explanation in the README seems to be as follows:

git clone https://github.com/XcodesOrg/xcodes
cd xcodes
- make install
+ sudo make install
# or, if /usr/local/ isn't in your PATH
- PREFIX=/your/install/directory make install
+ PREFIX=/your/install/directory sudo -E make install