pidgin/pidgin

Add some missed docs for PidginCredential*

2021-05-13, Elliott Sales de Andrade
7e8c50c967bc
Add some missed docs for PidginCredential*

* Add `Since` tags for `PidginCredential`.
* Add docs for `PidginCredential*` top-level API.

Testing Done:
Compile

Reviewed at https://reviews.imfreedom.org/r/651/
---
id: im.pidgin.Finch3
runtime: org.gnome.Platform
runtime-version: '3.36'
sdk: org.gnome.Sdk
command: finch3
finish-args:
- --share=ipc
- --socket=x11
- --share=network
- --talk-name=org.freedesktop.Notifications
- --system-talk-name=org.freedesktop.Avahi
modules:
- packaging/flatpak/libpurple-common.yml
- packaging/flatpak/libgnt.yml
- name: finch3
buildsystem: meson
config-opts:
- -Dgtkui=false
- -Ddoc=false
sources:
- type: dir
path: '.'