Update README.md and add CONTRIBUTING.md

- update supported CPU architectures
- update build instructions
- move contributing to a dedicated page

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+# Contributing
+
+## Testing
+
+After any change to the detection routines or match tables, it's always
+a good idea to run `make test`. If some test fails, and you're confident
+that the test is wrong and needs fixing, run `make fix-tests`.
+
+You can also add a new test (which is basically a file containing
+the raw CPUID data and the expected decoded items) by using
+`tests/create_test.py`. The workflow there is as follows:
+
+1. Run "cpuid_tool" with no arguments. It will tell you that it
+   has written a pair of files, raw.txt and report.txt. Ensure
+   that report.txt contains meaningful data.
+2. Run "tests/create_test.py raw.txt report.txt > «my-cpu».test"
+3. Use a proper descriptive name for the test (look into tests/amd
+   and tests/intel to get an idea) and copy your test file to an
+   appropriate place within the tests directory hierarchy.
+
+AIDA64 CPUID dumps (mostly found on [InstLatx64](http://instlatx64.atw.hu/)) are also supported.
+To create a new test based on a AIDA64 CPUID dump, you can do:
+```shell
+cpuid_tool --load=aida64_raw.txt --outfile=report.txt --report
+./tests/create_test.py aida64_raw.txt report.txt > tests/xxx/yyy/my-cpu.test
+```
+
+For non-developers, who still want to contribute tests for the project,
+use [this page](http://libcpuid.sourceforge.net/bugreport.php) to report
+misdetections or new CPUs that libcpuid doesn't handle well yet.