Add README.md file.

Signed-off-by: Jiri Slachta <slachta@cesnet.cz>

README.md

+# Telephony packages feed
+
+## Description
+
+This is an OpenWrt package feed containing community maintained telephony packages.
+
+## Usage
+
+To use these packages, add the following line to the feeds.conf
+in the OpenWrt buildroot:
+
+```
+src-git telephony https://github.com/openwrt/telephony.git
+```
+
+This feed should be included and enabled by default in the OpenWrt buildroot. To install all its package definitions, run:
+
+```
+./scripts/feeds update telephony
+./scripts/feeds install -a -p telephony
+```
+
+The telephony packages should now appear in menuconfig.