Make sure examples link properly.

examples/Makefile

@@ -22,10 +22,10 @@ protoc_middleman: addressbook.proto
 	@touch protoc_middleman
 
 add_person_cpp: add_person.cc protoc_middleman
-	c++ add_person.cc addressbook.pb.cc -lprotobuf -o add_person_cpp
+	c++ add_person.cc addressbook.pb.cc -lprotobuf -lpthread -o add_person_cpp
 
 list_people_cpp: list_people.cc protoc_middleman
-	c++ list_people.cc addressbook.pb.cc -lprotobuf -o list_people_cpp
+	c++ list_people.cc addressbook.pb.cc -lprotobuf -lpthread -o list_people_cpp
 
 javac_middleman: AddPerson.java ListPeople.java protoc_middleman
 	javac AddPerson.java ListPeople.java com/example/tutorial/AddressBookProtos.java

examples/README.txt

@@ -15,7 +15,7 @@ creates the following executable files in the current directory:
   add_person_java    list_people_java
   add_person_python  list_people_python
 
-If you only want to compile examples in one language, use "make cpp",
+If you only want to compile examples in one language, use "make cpp"*,
 "make java", or "make python".
 
 All of these programs simply take an address book file as their parameter.
@@ -23,3 +23,7 @@ The add_person programs will create the file if it doesn't already exist.
 
 These examples are part of the Protocol Buffers tutorial, located at:
   http://code.google.com/apis/protocolbuffers/docs/tutorials.html
+
+* Note that on some platforms you may have to edit the Makefile and remove
+"-lpthread" from the linker commands (perhaps replacing it with something else).
+We didn't do this automatically because we wanted to keep the example simple.