Manual: anonymous function in pipeline needs parentheses (#43661)
Consider:
```julia
d = (1:10
.|> x -> x^2
|> sum
)
```
This seems to compute a sum of squares.
But it does not. It outputs a vector of squares. (Because `|> sum` is parsed as being part of the anonymous function's body).
Parentheses are needed for the desired (expected?) behaviour:
```julia
d = (1:10
.|> (x -> x^2)
|> sum
)
```
This PR adds a small note and example to the "Function composition and piping" section of the manual to flag this.
As an aside, this confusion is even present in the [docstring](https://docs.julialang.org/en/v1/base/base/#Base.:|%3E) for `|>`:
> Applies a function to the preceding argument. This allows for easy function chaining.
> ```julia
[1:5;] |> x->x.^2 |> sum |> inv
```
This is parsed as
```julia
[1:5;] |> x-> (x.^2 |> sum |> inv)
```
but it feels like the author meant
```julia
[1:5;] |> (x-> x.^2) |> sum |> inv)
```.
