Cross compile and README update

.gitignore

@@ -24,4 +24,5 @@ _testmain.go
 *.prof
 
 /gopow
+/build
 resources.go

Makefile

@@ -4,7 +4,7 @@
 VERSION = $(shell git describe --always --dirty)
 TIMESTAMP = $(shell git show -s --format=%ct)
 
-default: build
+default: build_darwin
 
 setup: 
 	go get -u github.com/jteeuwen/go-bindata/...
@@ -12,13 +12,34 @@ setup:
 resources:
 	go-bindata -pkg resources -o internal/resources/resources.go resources/...
 
-build: resources
+build_darwin: resources
-	go build -o ./gopow *.go
+	GOOS=darwin GOARCH=amd64 go build -a -o ./build/gopow *.go
+	zip ./build/gopow_darwin64.zip ./build/gopow
+
+build_linux: resources
+	GOOS=linux GOARCH=amd64 go build -a -o ./build/gopow *.go
+	zip ./build/gopow_linux64.zip ./build/gopow
+
+build_arm5: resources
+	GOOS=linux GOARM=5 GOARCH=arm go build -a -o ./build/gopow *.go
+	zip ./build/gopow_linux_arm5.zip ./build/gopow
+
+build_arm7: resources
+	GOOS=linux GOARM=7 GOARCH=arm go build -a -o ./build/gopow *.go
+	zip ./build/gopow_linux_arm7.zip ./build/gopow
+
+build_win: resources
+	GOOS=windows GOARCH=amd64 go build -a -o ./build/gopow.exe *.go
+	zip ./build/gopow_win64.zip ./build/gopow.exe
+
+all: build_darwin build_linux build_arm5 build_arm7 build_win
+	rm ./build/gopow
+	rm ./build/gopow.exe
 
 lint:
 	golint .
 
 clean:
-	rm -f gopow
+	rm -f build
 	rm -rf internal/resources
 

README.md

@@ -1,2 +1,28 @@
 # rtl-gopow
 Render tables from rtl_power to a nice heat map
+Here is an render of rtl_power tool scanning 80-90 MHz during 2.5 hours moving in a car. ![80-90 MHz](http://i.imgur.com/knkzLXO.jpg).
+
+# Availability
+Since Go is easy to cross compile, this tool can be easily distributed as a binary without any dependencies. You'll find it under Releases here on github. The following platforms are avalible as a ready to run binary file:
+
+* OS X (x64)
+* Linux (x64)
+* Linux (arm5)
+* Linux (arm7)
+* Windows (x64)
+
+## Performance
+A render of a 600 MB csv file takes about 2 minutes on a 2,4 GHz Intel Core i5. There is still lots of room for improvement on that though. Memory usage is quite horrid.
+
+## Options
+```
+GLOBAL OPTIONS:
+   --input, -i      CSV input file generated by rtl_power [required]
+   --output, -o     Output file, default same as input file with new extension
+   --format, -f 'png'   Output file format, default png [png,jpeg]
+   --verbose        Enable more verbose output
+   --no-annotations Disabled annotations such as time and frequency scales
+   --help, -h       show help
+   --version, -v    print the version
+
+   ```