Updates the error output for an empty directory (#5610)

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**What type of PR is this:**

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**What does this PR do / why we need it:**

Updates the error output for running `odo dev` or `odo deploy` in an
empty directory. Telling the user to run the same command in a non-empty
dir, OR use `odo init`.

**Which issue(s) this PR fixes:**
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N/A

**PR acceptance criteria:**

- [X] Unit test

- [X] Integration test

- [X] Documentation

**How to test changes / Special notes to the reviewer:**

Signed-off-by: Charlie Drage <[email protected]>

pkg/odo/cli/deploy/deploy.go

@@ -65,7 +65,7 @@ func (o *DeployOptions) Complete(cmdline cmdline.Cmdline, args []string) (err er
 		return err
 	}
 	if isEmptyDir {
-		return errors.New("this command cannot run in an empty directory, you need to run it in a directory containing source code")
+		return errors.New("this command cannot run in an empty directory, run the command in a directory containing source code or initialize using 'odo init'")
 	}
 
 	initFlags := o.clientset.InitClient.GetFlags(cmdline.GetFlags())

pkg/odo/cli/dev/dev.go

@@ -90,7 +90,7 @@ func (o *DevOptions) Complete(cmdline cmdline.Cmdline, args []string) error {
 		return err
 	}
 	if isEmptyDir {
-		return errors.New("this command cannot run in an empty directory, you need to run it in a directory containing source code")
+		return errors.New("this command cannot run in an empty directory, run the command in a directory containing source code or initialize using 'odo init'")
 	}
 	initFlags := o.clientset.InitClient.GetFlags(cmdline.GetFlags())
 	err = o.clientset.InitClient.InitDevfile(initFlags, o.contextDir,