Added beta warnings to README.

Author: todofixthis

README.rst

@@ -4,6 +4,10 @@
 =====
 PyOTA
 =====
+.. warning::
+   ⚠️ This is pre-release software; it may have performance or stability issues.
+   Please do not use this software on mainnet until v2.0.0 stable is released. ⚠️
+
 This is the official Python library for the IOTA Core.
 
 It implements both the `official API`_, as well as newly-proposed functionality
@@ -28,9 +32,13 @@ PyOTA is compatible with Python 3.6, 3.5 and 2.7.
 ============
 Installation
 ============
+.. warning::
+   ⚠️ This is pre-release software; it may have performance or stability issues.
+   Please do not use this software on mainnet until v2.0.0 stable is released. ⚠️
+
 To install the latest version::
 
-  pip install pyota
+  pip install --pre pyota
 
 Optional C Extension
 ====================
@@ -39,7 +47,7 @@ cryptography features significantly (speedups of **60x** are common!).
 
 To install this extension, use the following command::
 
-   pip install pyota[ccurl]
+   pip install --pre pyota[ccurl]
 
 
 Installing from Source