Support running commands in repositories without action.yaml (#293)

* Comment for public function

* Add git describe fallback

* spelling: github

* Set initial branch to satisfy tests for modern git

* Clarify -even- if

* Go 1.16

* Support running commands in repositories without action.yaml

Support runnings commands with only a Docker file

Co-authored-by: Casey Lee <cplee@nektos.com>

pkg/runner/res/trampoline.js

@@ -0,0 +1,14 @@
+const { spawnSync } = require('child_process')
+const spawnArguments={
+  cwd: process.env['INPUT_CWD'],
+  stdio: [
+    process.stdin,
+    process.stdout,
+    process.stderr,
+  ]
+}
+const child=spawnSync(
+  '/bin/sh',
+  [ '-c' ].concat(process.env['INPUT_COMMAND']),
+  spawnArguments)
+process.exit(child.status)