mark the minimum supported Linux kernel version

This is just taken from the binary itself. It would be nice to mark the
minimum glibc version too, and the corresponding RHEL/CentOS version.

Author: thestinger

README.md

@@ -72,7 +72,7 @@ fetch snapshots, and an OS that can execute the available snapshot binaries.
 Snapshot binaries are currently built and tested on several platforms:
 
 * Windows (7, 8, Server 2008 R2), x86 only
-* Linux (various distributions), x86 and x86-64
+* Linux (2.6.18 or later, various distributions), x86 and x86-64
 * OSX 10.7 (Lion) or greater, x86 and x86-64
 
 You may find that other platforms work, but these are our officially

doc/tutorial.md

@@ -73,7 +73,7 @@ from the Internet on our supported platforms.
 Snapshot binaries are currently built and tested on several platforms:
 
 * Windows (7, 8, Server 2008 R2), x86 only
-* Linux (various distributions), x86 and x86-64
+* Linux (2.6.18 or later, various distributions), x86 and x86-64
 * OSX 10.7 (Lion) or greater, x86 and x86-64
 
 You may find that other platforms work, but these are our "tier 1"