README.md adjustments (and a few more minor things)

[qmonnet]

• README.md: Use Option to pass programs when building new VMs in examples
• README.md: Fix example by using an existing object file
• README.md: Adjust Windows execution for examples with JIT compiler
• src/lib.rs: Make "cargo test" run on examples from README.md
• README.md: Add coverage status badge
• README.md: State DCO requirement explicitly
• examples/rbpf_plugin.rs: Fix minor reports from clippy

[60ke]

great,It looks like my code submission is too incomplete. I have learned a lot,thanks

[qmonnet]

I was looking at how to run the tests on the README and only noticed the missing occurrences after merging your PR :)