golangci: enable GoDoc linting

golint is scoring pretty low currently, because many exported
functions and variables are missing a well-formatted GoDoc comment:

https://goreportcard.com/report/github.com/opencontainers/runc

Note that `golint` has been depracted, and replaced by `revive`:

    level=warning msg="[runner] The linter 'golint' is deprecated (since v1.41.0) due to: The repository of the linter has been archived by the owner.  Replaced by revive."

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.golangci.yml

@@ -7,3 +7,8 @@ run:
 linters:
   enable:
     - gofumpt
+    - revive
+
+issues:
+  include:
+    - EXC0002