Add note about PyCrypto and ecdsa

1 files changed, 3 insertions, 1 deletions

diff --git a/README.md b/README.md
index e76872d..383ad71 100644
--- a/README.md
+++ b/README.md
@@ -15,13 +15,15 @@ $ pip install PyJWT
 
 **A Note on Dependencies**:
 
-RSA and ECDSA signatures depend on the cryptography package. If you plan on
+RSA and ECDSA signatures depend on the recommended `cryptography` package. If you plan on
 using any of those algorithms, you'll need to install it as well.
 
 ```
 $ pip install cryptography
 ```
 
+If you're system doesn't allow installing `cryptography` like on Google App Engine, you can install `PyCrypto` for RSA signatures and `ecdsa` for ECDSA signatures.
+
 ## Usage
 
 ```python