README: Let dependencies be installed systemwide

Use sudo for make & make install. This is required for installing
natively.

Change-Id: Ib5af91871aade4c18669e6e5cf88374f14dfbb69
Tested: Ubuntu 16.04.2 LTS (native install)

README.md

@@ -49,7 +49,7 @@ cd LAStools/LASzip
 mkdir build
 cd build
 cmake -DCMAKE_BUILD_TYPE=Release ..
-make && make install
+sudo make && sudo make install
 ldconfig
 
 git clone https://github.com/pierotofy/PotreeConverter /staging/PotreeConverter
@@ -57,7 +57,7 @@ cd /staging/PotreeConverter
 mkdir build
 cd build
 cmake -DCMAKE_BUILD_TYPE=Release -DLASZIP_INCLUDE_DIRS=/staging/LAStools/LASzip/dll -DLASZIP_LIBRARY=/staging/LAStools/LASzip/build/src/liblaszip.so ..
-make && make install
+sudo make && sudo make install
 ```
 2) Install gdal2tiles.py script, node.js and npm dependencies