Update readme with correct CUDA versions (#8315)

Replaces CUDA 10.1/10.2 with 11.0/11.2.

Authors:
  - Ray Douglass (https://github.com/raydouglass)

Approvers:
  - AJ Schmidt (https://github.com/ajschmidt8)

URL: #8315

README.md

@@ -67,13 +67,13 @@ cuDF can be installed with conda ([miniconda](https://conda.io/miniconda.html),
 
 For `cudf version == 21.06` :
 ```bash
-# for CUDA 10.1
+# for CUDA 11.0
 conda install -c rapidsai -c nvidia -c numba -c conda-forge \
-    cudf=21.06 python=3.7 cudatoolkit=10.1
+    cudf=21.06 python=3.7 cudatoolkit=11.0
 
-# or, for CUDA 10.2
+# or, for CUDA 11.2
 conda install -c rapidsai -c nvidia -c numba -c conda-forge \
-    cudf=21.06 python=3.7 cudatoolkit=10.2
+    cudf=21.06 python=3.7 cudatoolkit=11.2
 
 ```