Update README.md

Author: SimonDanisch

README.md

@@ -8,4 +8,22 @@
 
 Remove jit overhead from your package and compile it into a system image.
 
-Usage Example in [Makie](https://github.com/SimonDanisch/Makie.jl/blob/master/deps/build.jl)
+## Usage Example
+E.g. do:
+```Julia
+using PackageCompiler
+
+# This command will use the runtest.jl of Matcha + UnicodeFun to find out what functions to precompile!
+# force = false to not force overwriting julia's current system image
+PackageCompiler.compile_package("Matcha", "UnicodeFun", force = false, reuse = false) 
+
+# build again, with resuing the snoop file
+PackageCompiler.compile_package("Matcha", "UnicodeFun", force = false, reuse = true)
+
+# You can define a file that will get run for snooping explicitely like this:
+# this makes sure, that binary gets cached for all functions called in `for_snooping.jl`
+PackageCompiler.compie_package(("Matcha", "relative/path/for_snooping.jl"))
+
+# if you used force and want your old system image back (force will overwrite the default system image Julia uses) you can run:
+PackageCompiler.revert() 
+```