update README

Major code changes

1) Added time string to top result
2) Improved netstat output format
3) Return 127.0.0.1 instead of panic while error happens
4) vmstat implementation
5) vmstat fixed build error
6) Added command top from procps
7) Added tags configured in the YAML to meta-info request for action API
8) Socket timeout while reading response from OpenJ9 VM
9) Fixed toph2 error continue instead of break when error happens
10) Full thread dump to thread dump
11) jattach: change timeout to 30 minutes
12) Support timestamp override as value in m3-fin response
13) Fixed stuck process while capturing Kernel data