Update docs with the details of multiple HTTPProviders

Author: kclowes

docs/providers.rst

@@ -124,9 +124,10 @@ HTTPProvider
         >>> from web3 import Web3
         >>> w3 = Web3(Web3.HTTPProvider("http://127.0.0.1:8545"))
 
-    Note that you should create only one HTTPProvider per python
-    process, as the HTTPProvider recycles underlying TCP/IP network connections,
-    for better performance.
+    Note that you should create only one HTTPProvider with the same provider URL
+    per python process, as the HTTPProvider recycles underlying TCP/IP
+    network connections, for better performance. Multiple HTTPProviders with different
+    URLs will work as expected.
 
     Under the hood, the ``HTTPProvider`` uses the python requests library for
     making requests.  If you would like to modify how requests are made, you can