Update help message

More helpful help message now that there's an increasing number of ways to use fSpy from the command line. Displays various use cases, vaguely following the docopt style.

src/cli/cli.ts

@@ -24,28 +24,35 @@ import Solver from '../gui/solver/solver'
 import { ImageState } from '../gui/types/image-state'
 import { SolverResult } from '../gui/solver/solver-result'
 
+const helpMessage = `\
+Usage:
+  fSpy (-h | --help)
+   Show this help message
+
+  fSpy [--open <imgPath>] [--wd <folderPath>]
+   Open fSpy in GUI mode. Optional arguments to load an image and
+   set a default working directory.
+
+  fSpy -w <width> -h <height> -s <statePath> -o <resultPath>
+   CLI mode. The fSpy CLI is used to compute camera parameters
+   without using the GUI. Image data is not used for this process,
+   only the image dimensions are required.
+
+Options:
+    -w  The width of the input image.
+    -h  The height of the input image.
+    -s  Path to a JSON file with project state data, the shape
+        of which is described by the SavedState interface.
+    -o  A path to write the solver result to. The shape of
+        the data is described by the SolverResult interface.
+--open  A path to an image file for fSpy to load on launch
+  --wd  A path to a folder, for all open/save dialogs to open to
+        by default.
+`
 export class CLI {
 
   static printUsage() {
-    console.log('fSpy CLI')
-    console.log('')
-    console.log('The fSpy CLI is used to compute camera parameters without')
-    console.log('using the GUI. The image data is not used for this process.')
-    console.log('Only the image dimensions are required.')
-    console.log('')
-    console.log('To show this help text, pass -h or --help as the only option')
-    console.log('')
-    console.log('Options (all required)')
-    console.log('  -w')
-    console.log('     The width of the input image.')
-    console.log('  -h')
-    console.log('     The height of the input image.')
-    console.log('  -s')
-    console.log('     Path to a JSON file with project state data, the shape')
-    console.log('     of which is described by the SavedState interface.')
-    console.log('  -o')
-    console.log('     A path to write the solver result to. The shape of')
-    console.log('     the data is described by the SolverResult interface.')
+    console.log(helpMessage)
   }
 
   static run(argv: string[]) {