Adding Gentoo Install section (#764)

* Adding Gentoo Install section

* Adding the relevant links to check ebuild source code, contact maintainers and file bug reports

README.md

@@ -147,6 +147,28 @@ The AUR [Release Package](https://aur.archlinux.org/packages/auto-cpufreq) is cu
 - The GNOME Power Profiles daemon is [automatically disabled by auto-cpufreq-installer](https://github.com/AdnanHodzic/auto-cpufreq#1-power_helperpy-script-snap-package-install-only) due to it's conflict with auto-cpufreq.service. However, this doesn't happen with AUR installs, which can lead to problems (e.g., [#463](https://github.com/AdnanHodzic/auto-cpufreq/issues/463)) if not masked manually.
   - Open a terminal and run `sudo systemctl mask power-profiles-daemon.service` (then `enable` and `start` the auto-cpufreq.service if you haven't already).
 
+### Gentoo Linux (GURU Repository)
+
+New versions of auto-cpufreq were recently added to GURU, Gentoo's official community-maintained ebuild repository. The [ebuild](https://github.com/gentoo-mirror/guru/tree/master/sys-power/auto-cpufreq) is maintaned by [S41G0N](https://github.com/S41G0N) and other [GURU contributors](https://bugs.gentoo.org), who can respond in case of issues.
+
+In order to build auto-cpufreq, it is necessary to add & sync GURU repository first. Adding ~amd64 keyword is also needed to unmask the package.
+
+``` 
+# echo "sys-power/auto-cpufreq ~amd64" >> /etc/portage/package.accept_keywords
+# eselect repository enable guru
+# emaint sync -r guru
+# emerge --ask auto-cpufreq
+```
+
+**Notices**
+
+- The build process links to `/usr/share/` instead of `/usr/local/share/`
+- The build works on both systemd/OpenRC systems (both systemd and OpenRC will have a service called auto-cpufreq which can be started automatically)
+- The daemon installer provided does work, but it is RECOMMENDED to install the daemon with:
+``` 
+# systemctl enable --now auto-cpufreq 
+# rc-update add auto-cpufreq default && rc-service auto-cpufreq start
+```
 
 ### NixOS