DOC: Suggest -j N if more than one CPU available

README.md

@@ -63,6 +63,7 @@ For Linux x86_64 and Mac OSX, try the following.
     $ make all
     $ make check
 
+Consider using `make -j N` where N is the number of jobs to run simultaneously.
 The last command runs a test suite. Each testing step is reported if the
 environment variable VERBOSE is set to 1.  E.g., try `VERBOSE=1 make check`.
 Finally,

doc/installation.md

@@ -16,6 +16,11 @@ definition in Makefile).  The parser generator
 [flex](http://flex.sourceforge.net/) are required to build gr1c.  Other Yacc and
 lex compatible tools may suffice, but this has not been tested.
 
+If the machine on which you are building has more than one CPU, then building
+time may be reduced by running more than one Make job simultaneously. To do
+this, use the switch `-j N` in `make` commands in these instructions, where `N`
+is the number of jobs. E.g., if there are 8 CPUs available, `make -j 8 all`.
+
 
 Building
 --------