README: explain functionality, and add section about building from releases

Author: rofl0r

README.md

@@ -1,6 +1,23 @@
 MacGeiger - a WIFI AP locator utility
 =====================================
 
+this tool puts your wireless card into monitor mode, then processes beacon
+frames from APs to create a list, in which you can navigate with the cursor
+keys, then select one AP with `ENTER`. the AP will open in detail view and
+start to beep. the faster it beeps, the better is the signal of the AP.
+
+this is quite handy to adjust directional antennas for the perfect signal
+without having to stare at a screen, which may be impractical.
+
+it can also be used on a mobile linux device (think netbook) to move through
+the streets and find the physical location of APs. you probably should wear
+headphones to do so...
+
+the keys `+`/`-` and `0`/`9` can be used to adjust the audio volume.
+
+Dependencies
+------------
+
 3rd party dependencies (install them including headers, i.e. -dev package)
 - libpcap :packet capturing library
 - libao   :audio output library
@@ -11,8 +28,20 @@ MacGeiger - a WIFI AP locator utility
 - concol  :terminal library with ncurses,termbox and SDL backends
   - depends on either SDL or ncurses devel package installed
 
-how to build:
--------------
+how to build from release tarball:
+----------------------------------
+
+just run `make`. if you need to change variables, CFLAGS, etc, do so by
+creating a file called `config.mak' and override the settings there.
+you may also use it to change `BACKEND` to `SDL`.
+by default the ncurses version will be built since it is assumed it is more
+widely available.
+
+Note: you may find release tarballs attached to git tags in the github repo.
+
+how to build from git:
+----------------------
+
 paste this into your shell
 
     mkdir /tmp/macgeiger-build
@@ -26,6 +55,9 @@ paste this into your shell
 if you want to use the ncurses backend (which is much harder to debug using gdb),
 replace SDL_CONSOLE with NCURSES_CONSOLE in the above printf command
 
+alternatively you may use the `create-dist` script to create a source tarball
+that does not require the rcb build tool.
+
 rebuilding with a different console backend:
 -------------------------------------------
 if you decided to try another backend (not the previously used one), run