Correct README description of E'.

src/bls12_381/README.md

@@ -34,7 +34,7 @@ Our extension field tower is constructed as follows:
 2. F<sub>q<sup>6</sup></sub> is constructed as F<sub>q<sup>2</sup></sub>(v) / (v<sup>3</sup> - ξ) where ξ = u + 1
 3. F<sub>q<sup>12</sup></sub> is constructed as F<sub>q<sup>6</sup></sub>(w) / (w<sup>2</sup> - γ) where γ = v
 
-Now, we instantiate the elliptic curve E(F<sub>q</sub>) : y<sup>2</sup> = x<sup>3</sup> + 4, and the elliptic curve E'(F<sub>q<sup>2</sup></sub>) : y<sup>2</sup> = x<sup>3</sup> + 4v.
+Now, we instantiate the elliptic curve E(F<sub>q</sub>) : y<sup>2</sup> = x<sup>3</sup> + 4, and the elliptic curve E'(F<sub>q<sup>2</sup></sub>) : y<sup>2</sup> = x<sup>3</sup> + 4(u + 1).
 
 The group G<sub>1</sub> is the *r* order subgroup of E, which has cofactor (x - 1)<sup>2</sup> / 3. The group G<sub>2</sub> is the *r* order subgroup of E', which has cofactor (x<sup>8</sup> - 4x<sup>7</sup> + 5x<sup>6</sup> - 4x<sup>4</sup> + 6x<sup>3</sup> - 4x<sup>2</sup> - 4x + 13) / 9.