add a few useful infos in README

README.md

@@ -0,0 +1,18 @@
+# GOG Downloader
+
+This repository contains the code of unofficial [GOG](http://www.gog.com/) downloader.
+
+## Build and install
+
+Under Debian/Ubuntu, first install dependencies:
+
+    apt install build-essential libcurl4-openssl-dev libboost-regex-dev libjsoncpp-dev liboauth-dev librhash-dev libtinyxml-dev libhtmlcxx-dev libboost-system-dev libboost-filesystem-dev libboost-program-options-dev libboost-date-time-dev help2man
+
+then
+
+    make
+    sudo make install
+
+## Use
+
+    man lgogdownloader