update examples with difficulty stars

examples/textures/textures_srcrec_dstrec.c

@@ -2,6 +2,8 @@
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 *   raylib [textures] example - Texture source and destination rectangles
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+*   Example complexity rating: [★★★☆] 3/4
+*
 *   Example originally created with raylib 1.3, last time updated with raylib 1.3
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 *   Example licensed under an unmodified zlib/libpng license, which is an OSI-certified,