Add built-in effects documentation (57 pages)
- Built-in-Effects.md: index page listing all 57 effects with descriptions
- Effect-*.md: one page per effect with full parameter table, ranges,
and usage tips (sourced from xLights src-core/effects/ source files)
Effects covered: Adjust, Bars, Butterfly, Candle, Circles, ColorWash,
Curtain, DMX, Duplicate, Faces, Fan, Fill, Fire, Fireworks, Galaxy,
Garlands, Glediator, Guitar, Kaleidoscope, Life, Lightning, Lines, Liquid,
Marquee, Meteors, Morph, MovingHead, Music, Off, On, Piano, Pictures,
Pinwheel, Plasma, Ripple, Servo, Shader, Shape, Shimmer, Shockwave,
SingleStrand, Sketch, Snowflakes, Snowstorm, Spirals, Spirograph, State,
Strobe, Tendril, Text, Tree, Twinkle, VUMeter, Video, Warp, Wave
All pages include a last-updated date footer.