Documentation: FAQ: drop shadow

NOTRY=true
DOCS_PREVIEW= https://skia.org/user/tips?cl=1918833003#text-shadow
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1918833003

Review URL: https://codereview.chromium.org/1918833003

site/user/tips.md

diff --git a/site/user/tips.md b/site/user/tips.md
index 91d1de5..25686df 100644
--- a/site/user/tips.md
+++ b/site/user/tips.md
@@ -7,6 +7,7 @@
 +   [How to add hardware acceleration in Skia](#hw-acceleration)
 +   [Does Skia support Font hinting?](#font-hinting)
 +   [Does Skia shape text (kerning)?](#kerning)
++   [How do I add drop shadow on text?](#text-shadow)
 
 * * *
 
@@ -166,4 +167,37 @@
 [HarfBuzz](http://www.freedesktop.org/wiki/Software/HarfBuzz/) to
 generate the glyphs and their positions, including kerning.
 
+* * *
+
+<span id="text-shadow"></span>
+
+How do I add drop shadow on text?
+---------------------------------
+
+<!--?prettify lang=cc?-->
+
+    void draw(SkCanvas* canvas) {
+        const char text[] = "Skia";
+        const SkScalar radius = 2.0f;
+        const SkScalar xDrop = 2.0f;
+        const SkScalar yDrop = 2.0f;
+        const SkScalar x = 8.0f;
+        const SkScalar y = 52.0f;
+        const SkScalar textSize = 48.0f;
+        const uint8_t blurAlpha = 127;
+        canvas->drawColor(SK_ColorWHITE);
+        SkPaint paint;
+        paint.setAntiAlias(true);
+        paint.setTextSize(textSize);
+        SkPaint blur(paint);
+        blur.setAlpha(blurAlpha);
+        blur.setMaskFilter(SkBlurMaskFilter::Make(
+            kNormal_SkBlurStyle,
+            SkBlurMaskFilter::ConvertRadiusToSigma(radius), 0));
+        canvas->drawText(text, strlen(text), x + xDrop, y + yDrop, blur);
+        canvas->drawText(text, strlen(text), x, y, paint);
+    }
+
+<a href='https://fiddle.skia.org/c/@text_shadow'><img src='https://fiddle.skia.org/i/@text_shadow_raster.png'></a>
+
 <div style="margin-bottom:99%"></div>