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>

README.md

@@ -102,7 +102,7 @@ It will save that information to `~/.actrc`, please refer to [Configuration](#co
   -l, --list                            list workflows
   -P, --platform stringArray            custom image to use per platform (e.g. -P ubuntu-18.04=nektos/act-environments-ubuntu:18.04)
       --privileged                      use privileged mode
-  -p, --pull                            pull docker image(s) if already present
+  -p, --pull                            pull docker image(s) even if already present
   -q, --quiet                           disable logging of output from steps
   -r, --reuse                           reuse action containers to maintain state
   -s, --secret stringArray              secret to make available to actions with optional value (e.g. -s mysecret=foo or -s mysecret)