Step 1: Understanding the Concept:
The region is the part of the unit disk lying above (or on) the line $x+y=1$.
Step 2: Detailed Explanation:
The unit circle $x^2+y^2=1$ and line $x+y=1$ intersect at $(1,0)$ and $(0,1)$.
Area $=$ (quarter circle area) $-$ (area of triangle with vertices $(0,0),(1,0),(0,1)$)
$= \dfrac{\pi(1)^2}{4} - \dfrac{1}{2}(1)(1) = \dfrac{\pi}{4} - \dfrac{1}{2}$.
Step 3: Final Answer:
Area $= \dfrac{\pi}{4} - \dfrac{1}{2}$ sq units.