document camera movements

glsl/docs.js

Use the sliders on the left to change values used in the shader.
## Keyboard shortcuts
## Keyboard shortcuts and navigation
- \`Ctrl-Enter\` reruns the shader
- \`Ctrl-e\` toggles the editor
- \`Space\` toggles animation
- \`Ctrl-h\` toggles help
You can move around using keyboard and mouse.  Pressing W (or Up) moves the camera
forward, pressing S (or Down) moves it backwards.  By pressing the left mouse button
and moving the mouse, you can "look around" then use the keyboard to move in that
direction.
## Default uniforms
- \`uniform vec2 iResolution\`: resolution of the canvas