Precedence issue with using <= for assignment

[leonardt]

From Pat (#315 (comment)):

One thing to watch out for using <=

for i in range(N):
    I[i] <= main.J1[i] if i < 8 else 0

doesn't work since <= has lower precedence than x if p then y. This need to be written as

for i in range(N):
    I[i] <= (main.J1[i] if i < 8 else 0)

We should document this issue and consider where there's a way we can safeguard against it (e.g. AST visitor that checks for these cases and inserts the parenthesis or emits a warning).