README.md: sort dependencies, document smpp.pdu

This dependency is currently only mentioned in requirements.txt, it
makes sense to also document it here.

Change-Id: I89760dd4008829c91fafbd442483d076c92a7ed4
---
M README.md
1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/README.md b/README.md
index c3c5a25..7801283 100644
--- a/README.md
+++ b/README.md
@@ -73,19 +73,20 @@
 
 Please install the following dependencies:
 
+ - bidict
+ - cmd2 >= 1.5.0
+ - colorlog
+ - construct >= 2.9.51
+ - gsm0338
+ - jsonpath-ng
+ - packaging
+ - pycryptodomex
  - pyscard
  - pyserial
  - pytlv
- - cmd2 >= 1.5.0
- - jsonpath-ng
- - construct >= 2.9.51
- - bidict
- - gsm0338
  - pyyaml >= 5.1
+ - smpp.pdu (from `github.com/hologram-io/smpp.pdu`)
  - termcolor
- - colorlog
- - packaging
- - pycryptodomex
 
 Example for Debian:
 ```sh

