Add requests to requirements.txt (ultralytics#5112)

* Requirements updated

1. Requests added to requirements.txt. That might not be included in all docker base images, adding it to the requirements is safer.
2. Added a minimum version to Pandas. It's a good practice to have versions for all dependencies.

* Sort alphabetically

* Update requirements.txt

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

requirements.txt

@@ -6,6 +6,7 @@ numpy>=1.18.5
 opencv-python>=4.1.2
 Pillow>=7.1.2
 PyYAML>=5.3.1
+requests>=2.23.0
 scipy>=1.4.1
 torch>=1.7.0
 torchvision>=0.8.1
@@ -16,7 +17,7 @@ tensorboard>=2.4.1
 # wandb
 
 # Plotting ------------------------------------
-pandas
+pandas>=1.1.4
 seaborn>=0.11.0
 
 # Export --------------------------------------