Manual: updated installing with almost

[makedoc]

user-doc/Installation.txt

@@ -486,13 +486,24 @@ Compile it:
 \warning ALMOST needs SQLITE3 and  GZIP installed on your computer.
 \warning ALMOST cannot be installed in the same folder of the source code, use --prefix to install it in a different folder
 
+On Linux:
+
 \verbatim
 > ./configure --prefix="wherever you want it" CXXFLAGS="-O3 -fPIC" CFLAGS="-O3 -fPIC" LIBS=-llapack 
 > make
 > make install
 \endverbatim
-Configure can complain about lapack and RDCs but it doesn't matter.
+
+On OSX:
+\verbatim
+> ./configure --prefix="wherever you want it" CXXFLAGS="-O3" CFLAGS="-O3" 
+> make
+> make install
+\endverbatim
+
+The configuration can complain about lapack and RDCs but it doesn't matter.
 Sometimes ALMOST can give errors related to the automake tools. To fix them it is often enough to execute
+
 \verbatim
 > autoreconf -fi
 > automake