Update RedHat family install instructions.

README.md

@@ -84,7 +84,8 @@ etc):
     All Debian-derived distros require manual activation for policy
     reasons, please see `/usr/share/doc/autojump/README.Debian`.
 
--   RedHat, Fedora, CentOS
+-   RedHat, Fedora, CentOS (install `autojump-zsh` for zsh,
+    `autojump-fish` for fish, etc.)
 -   ArchLinux
 -   Gentoo
 -   Frugalware

docs/install.md

@@ -22,7 +22,8 @@ package management utilities to install (e.g. yum, apt-get, etc):
     All Debian-derived distros require manual activation for policy reasons,
     please see `/usr/share/doc/autojump/README.Debian`.
 
-- RedHat, Fedora, CentOS
+- RedHat, Fedora, CentOS (install `autojump-zsh` for zsh, `autojump-fish` for
+  fish, etc.)
 - ArchLinux
 - Gentoo
 - Frugalware