MAINT: add `.gitignore` for docs
Specifically, ignores the api directory that is built when compiling the docs. Without this, after building the docs, all of these files are marked as 'Untracked' which really clutters up the current changes.
Specifically, ignores the api directory that is built when compiling the docs. Without this, after building the docs, all of these files are marked as 'Untracked' which really clutters up the current changes.