docs(osv-linter): Add a README.md

[andrewpollock]

This commit adds a README.md to provide interested parties with some further details and guidance about the OSV linter

[andrewpollock]

@hogo6002 could you please also take a look at this and see how it reads for you as someone new to this?

[andrewpollock]

@darakian I'd appreciate your perspective on the readability of this, if you have time

[hogo6002]

@hogo6002 could you please also take a look at this and see how it reads for you as someone new to this?

LGTM! The Usage and Contributing sections are very helpful for new contributors like me.

[andrewpollock]

@oliverchang I'd like to get this merged today, so any feedback from @darakian I'll act on in a follow-up PR.

[darakian]

Looks quite readable to me, but two things come to mind

1. Install instructions would be nice. I know clone & compile is implicit given that it's a git repo , but if the go get <url> method of installation works then I would call that out specifically. If it doesn't work then getting it to work would be nice :)
2. Breaking the checks out into their own section with some prose describing what they do would be nice. Maybe more relevant once there are more than six checks.

[oliverchang]

apologies, missed your earlier comment @andrewpollock!