Tiny doc updates re yum/dnf etc

* INSTALL: Mention dnf and Debian unversioned emacs package.
* doc/misc/efaq.texi (Installing Emacs): Mention dnf.

INSTALL

@@ -202,8 +202,9 @@ The names of the packages that you need varies according to the
 GNU/Linux distribution that you use, and the options that you want to
 configure Emacs with.  On Debian-based systems, you can install all the
 packages needed to build the installed version of Emacs with a command
-like 'apt-get build-dep emacs24'.  On Red Hat systems, the
-corresponding command is 'yum-builddep emacs'.
+like 'apt-get build-dep emacs' (on older systems, replace 'emacs' with
+eg 'emacs25').  On Red Hat-based systems, the corresponding command is
+'dnf builddep emacs' (or older systems, use 'yum-builddep' instead).
 
 
 DETAILED BUILDING AND INSTALLATION:

doc/misc/efaq.texi

@@ -3362,8 +3362,9 @@ and binaries, and how to install Emacs on those systems.
 
 Most GNU/Linux distributions provide pre-built Emacs packages.
 If Emacs is not installed already, you can install it by running (as
-root) a command such as @samp{yum install emacs} (Red Hat and
-derivatives) or @samp{apt-get install emacs} (Debian and derivatives).
+root) a command such as @samp{dnf install emacs} (Red Hat and
+derivatives; use @samp{yum} in older distributions) or
+@samp{apt-get install emacs} (Debian and derivatives).
 
 If you want to compile Emacs yourself, read the file @file{INSTALL} in
 the source distribution.  In brief: