Initial action stub

Now that I know how to write some simple action, let's make a stub
more complete. For example, I already know what inputs I would like
to handle for this action.

action.yml

@@ -0,0 +1,20 @@
+name: Enable Developer Command Prompt
+description: Configure Microsoft Visual C++ command line
+inputs:
+  arch:
+    description: Target architecture
+    default: x64
+  sdk:
+    description: Windows SDK number to build for
+  spectre:
+    description: Enable Specre mitigations
+  toolset:
+    description: VC++ compiler toolset version
+  uwp:
+    description: Build for Universal Windows Platform
+runs:
+  using: node12
+  main: index.js
+branding:
+  icon: terminal
+  color: purple