add FAQ about version numbers

FAQ

@@ -10,6 +10,7 @@ OpenSSL  -  Frequently Asked Questions
 * Why aren't tools like 'autoconf' and 'libtool' used?
 * What is an 'engine' version?
 * How do I check the authenticity of the OpenSSL distribution?
+* How does the versioning scheme work?
 
 [LEGAL] Legal questions
 
@@ -173,6 +174,19 @@ just do:
 
    pgp TARBALL.asc
 
+* How does the versioning scheme work?
+
+After the release of OpenSSL 1.0.0 the versioning scheme changed. Letter 
+releases (e.g. 1.0.1a) can only contain bug and security fixes and no
+new features. Minor releases change the last number (e.g. 1.0.2) and 
+can contain new features that retain binary compatibility. Changes to
+the middle number are considered major releases and neither source nor
+binary compatibility is guaranteed.
+
+Therefore the answer to the common question "when will feature X be
+backported to OpenSSL 1.0.0/0.9.8?" is "never" but it could appear
+in the next minor release.
+
 [LEGAL] =======================================================================
 
 * Do I need patent licenses to use OpenSSL?