Added some useful build information

README.md

@@ -1,11 +1,27 @@
 ## Building
 
+You need to have some prerequisits:
+
+    apt install build-essential gawk unzip libncurses-dev libz-dev libssl-dev wget git subversion
+
 Check out this repository and execute `make`, i.e. like this:
 
     git clone https://github.com/ffrgb/site-ffrgb.git site-ffrgb
     cd site-ffrgb
     make
 
+### Quick Hints
+
+Some common useful parameters for make:
+
+    GLUON_TARGETS=ar71xx-generic - Only build the specified architecture
+    GLUON_GIT_REF=v2018.2.x - wich Gluon-Release version to build
+    FORCE_UNSAFE_CONFIGURE=1 - If You build as root in an disposable environment You don't care about
+    BROKEN=1 - Also build for untested but defined hardware wich may not work
+    V=s - Print more information
+
+Think about starting Your make process inside a `screen` session as it usually takes a long time to build.
+
 ## Further Resources
 
 Look at the [site configuration related Gluon documentation](http://gluon.readthedocs.org/en/v2016.2.3/user/site.html)