Rename `t5-large` to `t5-base` in README.md

examples/summarization/t5/README.md

-***This script evaluates the the multitask pre-trained checkpoint for ``t5-large`` (see paper [here](https://arxiv.org/pdf/1910.10683.pdf)) on the CNN/Daily Mail test dataset. Please note that the results in the paper were attained using a model fine-tuned on summarization, so that results will be worse here by approx. 0.5 ROUGE points***
+***This script evaluates the the multitask pre-trained checkpoint for ``t5-base`` (see paper [here](https://arxiv.org/pdf/1910.10683.pdf)) on the CNN/Daily Mail test dataset. Please note that the results in the paper were attained using a model fine-tuned on summarization, so that results will be worse here by approx. 0.5 ROUGE points***
 
 ### Get the CNN Data
 First, you need to download the CNN data. It's about ~400 MB and can be downloaded by