add more popcorn instructions

apps/popcorn/README.md

@@ -6,7 +6,7 @@ The compression format is not surprisingly not crazily advanced, so movie files
 
 Here is "Big Buck Bunny": https://drive.google.com/file/d/1q3szTVccPZ08v_TMDxy9ZgqeOOXXwHCX/view?usp=sharing which is 1.6GB
 
-### Using a movie
+### Writing a Movie to SD Card 
 
 These are raw disk images without a filesystem. These instructions assume a certain level of knowledge Please feel free to submit PRs
 to improve them!
@@ -19,6 +19,18 @@ A single movie can just be burned as the entirety of the SD card (via `dd` on un
 
 You can format the card with a GPT and then image movies onto the partitions (the partitions must obviously be big enough). The partition name from the GPT is used as the title for the movie.
 
+### Playback controls
+
+These are quite limited and use the 3 buttons on the VGA board, and use single button presses with function determined by how long the button is pressed before it is released.
+
+ * Short (<.25s) press while playing: `Slower : Pause : Faster`
+ * Short (<.25s) press while paused: `Step Backward : Play : Step Forward`
+ * Medium (<1s) press: `Previous File : Toggle Menu Display : Next File`
+ * Long (>1s) press: `Lower Volume : Toggle Play Direction : Higher Volume` - note you can hold the button down to continuosuly lower or raise volume.
+
+Pause and then unpause to reset playback speed to 1x
+
+
 ### Converting
 
 TODO - will upload a converter and instructions soon.