Adding template docs to the version command

Signed-off-by: Matt Farina <matt@mattfarina.com>

cmd/helm/version.go

@@ -39,6 +39,14 @@ version.BuildInfo{Version:"v2.0.0", GitCommit:"ff52399e51bb880526e9cd0ed8386f643
 - GitCommit is the SHA for the commit that this version was built from.
 - GitTreeState is "clean" if there are no local code changes when this binary was
   built, and "dirty" if the binary was built from locally modified code.
+
+When using the --template flag the following properties are available to use in
+the template:
+
+- .Version contains the semantic version of Helm
+- .GitCommit is the git commit
+- .GitTreeState is the state of the git tree when Helm was built
+- .GoVersion contains the version of Go that Helm was compiled with
 `
 
 type versionOptions struct {