[add] ProgressBar component

Ref #91

docs/components/ProgressBar.md

@@ -0,0 +1,23 @@
+# ProgressBar
+
+Display an activity progress bar.
+
+## Props
+
+[...View props](./View.md)
+
+**color**: string = '#1976D2'
+
+Color of the progress bar.
+
+**indeterminate**: bool = true
+
+Whether the progress bar will show indeterminate progress.
+
+**progress**: number
+
+The progress value (between 0 and 1).
+
+(web) **trackColor**: string = 'transparent'
+
+Color of the track bar.