Adds Gentoo Support

Uses extracted ISO hosted on sourceforge using this procedure:
http://blog.dastrup.com/?p=12

README.md

@@ -43,6 +43,7 @@ Full documentation is at ReadTheDocs:
 * [Debian](https://debian.org)
 * [Fedora](https://fedoraproject.org)
 * [FreeBSD](https://freebsd.org)
+* [Gentoo](https://gentoo.org)
 * [Kali Linux](https://www.kali.org)
 * [Mageia](http://www.mageia.org)
 * [OpenBSD](http://openbsd.org)

docs/index.md

@@ -47,6 +47,7 @@ You'll need to make sure to have [DOWNLOAD_PROTO_HTTPS](https://github.com/ipxe/
 * [Debian](https://debian.org)
 * [Fedora](https://fedoraproject.org)
 * [FreeBSD](https://freebsd.org)
+* [Gentoo](https://gentoo.org)
 * [Kali Linux](https://www.kali.org)
 * [Mageia](http://www.mageia.org)
 * [OpenBSD](http://openbsd.org)

src/gentoo.ipxe

@@ -0,0 +1,30 @@
+#!ipxe
+
+# Gentoo Operating System
+# http://www.gentoo.org
+
+# Note: in order to boot Gentoo via iPXE, the method at http://blog.dastrup.com/?p=12 has been utilized to 
+# to allow for the Gentoo minimal disk to boot.  I've regenerated the latest boot disks and have put
+# them on https://sourceforge.net/projects/netboot-xyz/files/distros/gentoo/amd64/20160204/
+
+goto ${menu}
+
+:gentoo
+set os gentoo
+menu Gentoo ${arch_a}
+item 20160204 Gentoo Minimal CD 20160204 (amd64)
+choose gentoo_version || goto gentoo_exit
+goto ${gentoo_version}
+
+:20160204
+set gentoopath https://sourceforge.net/projects/netboot-xyz/files/distros/gentoo/amd64/20160204
+echo Please note the gentoo ISO has been regenerated to work with iPXE
+echo using the method here: http://blog.dastrup.com/?p=12
+kernel --name gentoo-kernel ${gentoopath}/kernel/download root=/dev/ram0 init=/linuxrc loop=/image.squashfs looptype=squashfs cdroot=1 real_root=/
+initrd --name gentoo-initrd.img ${gentoopath}/initrd/download
+boot
+goto gentoo
+
+:gentoo_exit
+clear menu
+chain linux.ipxe

src/linux.ipxe

@@ -18,6 +18,7 @@ item --gap All Others:
 item antergos ${space} Antergos
 item architect ${space} Architect Linux
 item coreos ${space} CoreOS
+item gentoo ${space} Gentoo Linux
 item rancheros ${space} RancherOS
 item scientific ${space} Scientific
 item slackware ${space} Slackware