gst-python: add proper README and delete useless placeholder files

Fixes https://gitlab.freedesktop.org/gstreamer/gst-python/-/issues/54

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4693>

subprojects/gst-python/AUTHORS

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-This file will be autogenerated.  Please read README-docs.

subprojects/gst-python/README

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-This file will be autogenerated.  Please read README-docs.

subprojects/gst-python/README.md

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+# gst-python
+
+gst-python is an extension of the regular GStreamer Python bindings
+based on gobject-introspection information and PyGObject.
+
+It provides two things:
+
+1. "syntactic sugar" in form of overrides for various GStreamer APIs
+   that makes them easier to use in Python and more pythonic; and
+
+2. support for APIs that aren't available through the regular
+   gobject-introspection based bindings, such as e.g. GStreamer's
+   fundamental GLib types such as `Gst.Fraction`, `Gst.IntRange` etc.
+
+## Prerequisites
+
+These libraries are needed to build gst-python:
+ - gstreamer core
+ - gst-plugins-base
+ - pygobject
+
+You will also need pygobject and glib installed. On debian-based distros
+you can install these with:
+
+    sudo apt build-dep python3-gst-1.0
+
+Only Python 3 is supported.
+
+## Building
+
+    meson setup builddir && ninja -C builddir
+    meson install -C builddir
+
+## Using
+
+Once installed in the right place, you don't need to do anything in order
+to use the overrides. They will be loaded automatically on
+
+```python
+import gi
+gi.require_version('Gst', '1.0')
+gi.repository import GObject, Gst
+```
+
+Note that additional imports will be required for other GStreamer libraries to
+make use of their respective APIs, e.g. `GstApp` or `GstVideo`.
+
+## License
+
+gst-python is licensed under the [LGPL 2.1](https://www.gnu.org/licenses/lgpl-2.1.html)

subprojects/gst-python/TODO

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-Port old examples to GStreamer 1.0