build+docs: switch to python3, refresh FAQ and INSTALL documents

Refs: #5095
Change-Id: Icdc0e9463b28c07783edbe392a9bc47136947e3b
diff --git a/nfd.conf.sample.in b/nfd.conf.sample.in
index 4cd4e26..a17423f 100644
--- a/nfd.conf.sample.in
+++ b/nfd.conf.sample.in
@@ -177,7 +177,7 @@
   ;
   ; **Ubuntu:**
   ;
-  ;    sudo apt-get install libcap2-bin
+  ;    sudo apt install libcap2-bin
   ;
   ; **Mac OS X:**
   ;