Update INSTALL.md

INSTALL.md

@@ -8,13 +8,14 @@ If not, please read the instructions at [cornellev.github.io/icp/](https://corne
 > **Warning**: these instructions must be followed from start whenever an update to the installation is desired.
 
 1. The project uses CMake, but there is a Makefile provided for convenience.
-    Run `sudo make install` to install the library.
-    You can specify the installation locations by passing the `INSTALL_PREFIX` variable.
+2. Run `sudo make install` to install the library.
+    You can specify the installation locations by passing the `LIB_INSTALL` and `HEADER_INSTALL` variables.
     The default behavior is
-    ```sh
-    sudo make install INSTALL_PREFIX=/usr/local
     ```
-    which will install the library to `/usr/local/lib/libcevicp.a` and the headers in `/usr/local/include/cev_icp`.
+    sudo make install LIB_INSTALL=/usr/local/lib HEADER_INSTALL=/usr/local/include
+    ```
+    The library `libcevicp.a` will be located at `LIB_INSTALL`.
+    The header files will be accessible from `HEADER_INSTALL/cev_icp`, e.g., `HEADER_INSTALL/cev_icp/icp/icp.h`.
 2.  Run `sudo make uninstall` to remove the library.
     You can similarly pass the `INSTALL_PREFIX` variable, but it must be the same as where you installed.
     Note that uninstalling may leave some remanant directory structure.