docs: add CLI help

docs/cmd/tk_export_source.md

@@ -0,0 +1,32 @@
+## tk export source
+
+Export source commands
+
+### Synopsis
+
+Export source commands
+
+### Options
+
+```
+  -h, --help               help for source
+      --with-credentials   include credential secrets
+```
+
+### Options inherited from parent commands
+
+```
+      --all                  select all resources
+      --components strings   list of components, accepts comma-separated values (default [source-controller,kustomize-controller])
+      --kubeconfig string    path to the kubeconfig file (default "~/.kube/config")
+      --namespace string     the namespace scope for this operation (default "gitops-system")
+      --timeout duration     timeout for this operation (default 5m0s)
+      --verbose              print generated objects
+```
+
+### SEE ALSO
+
+* [tk export](tk_export.md)	 - Export commands
+* [tk export source git](tk_export_source_git.md)	 - Export git sources in YAML format
+
+###### Auto generated by spf13/cobra on 30-Apr-2020