Documentation/Changes: Now need OpenSSL devel packages for module signing

The module signing script (sign-file) used to be a wrapper around the
openssl program.  It has now been replaced by a C program that uses the
crypto library from the OpenSSL package meaning that the OpenSSL devel
packages are necessary to provide the devel library link and the header
files.

This would be openssl-devel on Fedora and libssl-dev on Debian.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: James Morris <james.l.morris@oracle.com>

Documentation/Changes

@@ -43,6 +43,7 @@ o  udev                   081                     # udevd --version
 o  grub                   0.93                    # grub --version || grub-install --version
 o  mcelog                 0.6                     # mcelog --version
 o  iptables               1.4.2                   # iptables -V
+o  openssl & libcrypto    1.0.1k                  # openssl version
 
 
 Kernel compilation
@@ -79,6 +80,17 @@ BC
 You will need bc to build kernels 3.10 and higher
 
 
+OpenSSL
+-------
+
+Module signing and external certificate handling use the OpenSSL program and
+crypto library to do key creation and signature generation.
+
+You will need openssl to build kernels 3.7 and higher if module signing is
+enabled.  You will also need openssl development packages to build kernels 4.3
+and higher.
+
+
 System utilities
 ================
 
@@ -295,6 +307,10 @@ Binutils
 --------
 o  <ftp://ftp.kernel.org/pub/linux/devel/binutils/>
 
+OpenSSL
+-------
+o  <https://www.openssl.org/>
+
 System utilities
 ****************
 
@@ -392,4 +408,3 @@ o  <http://oprofile.sf.net/download/>
 NFS-Utils
 ---------
 o  <http://nfs.sourceforge.net/>
-