typos in documentation

Created by: martinberoiz

Hi, I'm reading the documentation and I found a few things I think are mistakes

In table/io/#accessing-open-data-event-catalogues
```
GWOSC catalogues
For more details on the GWOSC catalogues, see https://www.gw-openscience.org/catalog/.
```
that link is a 404. Should be https://www.gw-openscience.org/eventapi/html/ instead.

In /segments/#combining-dataqualityflags

Union (|)
>>> a | b
returns the intersection of both the known and active segment lists, e.g:

I think it should say "returns the union of both..."

Same page
```
>>> ~a
returns the same known segments, and the inverse active segment lists, e.g:
```
I think it should say "returns the same known segments, and the complement active segment..." This may be too much of a nitpick tho.

In /detector/channel/

Alongside nomnitive attributes, each Channel has the following attributes:

I think it's nominative.

I can make a PR if you want.