Add 'Quickstart' section to README.md (#3)

Thanks for writing this up. I'll make a few minor changes to it after the merge.

README.md

@@ -17,6 +17,21 @@ This tool can be destructive and contain bugs, it will not let you overwrite the
 
  If a particular line in the input file is not supported by the parser, the tool will exit and print a link to submit an issue. If you are submitting an issue please attach a file that can reproduce the bug.
 
+## Quickstart
+
+After [installing go](https://golang.org/doc/install) (verify with `go version`, and don't forget the PATH steps), install and run this tool:
+
+```bash
+# Install
+go get github.com/jonnenauha/obj-simplify
+
+# Run
+obj-simplify -in <input-file> -out <output-file>
+
+# Help
+obj-simplify -h
+```
+
 ## Merging duplicate geometry
 
 Use `-eplison` to tune vector equality checks, the default is `1e-6`. This can have a positive impact especially on large OBJ files. Basic cleanup like trimming trailing zeros and converting -0 into 0 to reduce file size is also executed.