Docs revamp. Part 2

docs/source/topics/tgcrypto.rst

@@ -0,0 +1,32 @@
+Fast Crypto
+===========
+
+Pyrogram's speed can be *dramatically* boosted up by TgCrypto_, a high-performance, easy-to-install Telegram Crypto
+Library specifically written in C for Pyrogram [#f1]_ as a Python extension.
+
+TgCrypto is a replacement for the much slower PyAES and implements the crypto algorithms Telegram requires, namely
+**AES-IGE 256 bit** (used in MTProto v2.0) and **AES-CTR 256 bit** (used for CDN encrypted files).
+
+Installation
+------------
+
+.. code-block:: bash
+
+    $ pip3 install --upgrade tgcrypto
+
+.. note:: Being a C extension for Python, TgCrypto is an optional but *highly recommended* dependency; when TgCrypto is
+   not detected in your system, Pyrogram will automatically fall back to PyAES and will show you a warning.
+
+The reason about being an optional package is that TgCrypto requires some extra system tools in order to be compiled.
+The errors you receive when trying to install TgCrypto are system dependent, but also descriptive enough to understand
+what you should do next:
+
+-  **Windows**: Install `Visual C++ 2015 Build Tools <http://landinghub.visualstudio.com/visual-cpp-build-tools>`_.
+-  **macOS**: A pop-up will automatically ask you to install the command line developer tools.
+-  **Linux**: Install a proper C compiler (``gcc``, ``clang``) and the Python header files (``python3-dev``).
+-  **Termux (Android)**: Install ``clang`` and ``python-dev`` packages.
+
+.. _TgCrypto: https://github.com/pyrogram/tgcrypto
+
+.. [#f1] Although TgCrypto is intended for Pyrogram, it is shipped as a standalone package and can thus be used for
+   other Python projects too.