[3.14] gh-134370: Added clarification on instance annotations (GH-134387) (#134509)

gh-134370: Added clarification on instance annotations (GH-134387)

Instances of classes cannot have annotations,
however sometimes they will erroneously have the
__annotations__ attribute
(cherry picked from commit bd4046f4f869039a1a2ebe2d1d18bfbc2a2951b6)

Co-authored-by: Alex Kautz <alex@takemobi.com>