README: update content and use Markdown

The repository path changed and the information to manually add the feed
is outdated, since it enabled by default.

Also use Markdown to format the README since it looks much more
appealing.

Signed-off-by: Paul Spooren <mail@aparcar.org>
(cherry picked from commit 4bf9a5d5dc)

README

@@ -1,18 +0,0 @@
-This is an OpenWrt package feed containing community maintained routing packages.
-
-To use these packages, add the following line to the feeds.conf
-in the OpenWrt buildroot:
-
-  src-git routing git://github.com/openwrt-routing/packages.git
-  
-Update the feed:
-
-  ./scripts/feeds update routing
-  
-Activate the package:
-
-  ./scripts/feeds install -a -p routing
-  
-The routing packages should now appear in menuconfig.
-
-

README.md

@@ -0,0 +1,21 @@
+# OpenWrt Routing Feed
+
+## Description
+
+This OpenWrt package feed contains community maintained routing packages.
+
+## Usage
+
+
+This repository is intended to be layered on-top of an OpenWrt buildroot.
+If you do not have an OpenWrt buildroot installed, see the documentation at:
+[OpenWrt Buildroot – Installation][1] on the OpenWrt support site.
+
+This feed is enabled by default. To install all its package definitions, run:
+
+```
+./scripts/feeds update routing
+./scripts/feeds install -a -p routing
+```
+
+[1]: https://openwrt.org/docs/guide-developer/build-system/install-buildsystem