Fix Tasks examples

- Change prompt text to a string
- Change hardcoded `task='<OD>'` to `task=prompt`

These changes are necessary for most of the examples to work, and aligns the README with the Jupyter notebook examples.
These changes are also necessary in all of the other Florence-2 repos, but I'll only open the PR here since I don't want to spam PRs.

README.md

@@ -99,7 +99,7 @@ def run_example(prompt, text_input=None):
     )
     generated_text = processor.batch_decode(generated_ids, skip_special_tokens=False)[0]
 
-    parsed_answer = processor.post_process_generation(generated_text, task="<OD>", image_size=(image.width, image.height))
+    parsed_answer = processor.post_process_generation(generated_text, task=prompt, image_size=(image.width, image.height))
 
     print(parsed_answer)
 ```
@@ -113,7 +113,7 @@ Here are the tasks `Florence-2` could perform:
 ### OCR 
 
 ```python
-prompt = <OCR>
+prompt = '<OCR>'
 run_example(prompt)
 ```
 
@@ -121,25 +121,25 @@ run_example(prompt)
 OCR with region output format:
 {'\<OCR_WITH_REGION>': {'quad_boxes': [[x1, y1, x2, y2, x3, y3, x4, y4], ...], 'labels': ['text1', ...]}}
 ```python
-prompt = <OCR_WITH_REGION>
+prompt = '<OCR_WITH_REGION>'
 run_example(prompt)
 ```
 
 ### Caption
 ```python
-prompt = <CAPTION>
+prompt = '<CAPTION>'
 run_example(prompt)
 ```
 
 ### Detailed Caption
 ```python
-prompt = <DETAILED_CAPTION>
+prompt = '<DETAILED_CAPTION>'
 run_example(prompt)
 ```
 
 ### More Detailed Caption
 ```python
-prompt = <MORE_DETAILED_CAPTION>
+prompt = '<MORE_DETAILED_CAPTION>'
 run_example(prompt)
 ```
 
@@ -150,7 +150,7 @@ OD results format:
 'labels': ['label1', 'label2', ...]} }
 
 ```python
-prompt = <OD>
+prompt = '<OD>'
 run_example(prompt)
 ```
 
@@ -159,7 +159,7 @@ Dense region caption results format:
 {'\<DENSE_REGION_CAPTION>' : {'bboxes': [[x1, y1, x2, y2], ...], 
 'labels': ['label1', 'label2', ...]} }
 ```python
-prompt = <DENSE_REGION_CAPTION>
+prompt = '<DENSE_REGION_CAPTION>'
 run_example(prompt)
 ```
 
@@ -168,7 +168,7 @@ Dense region caption results format:
 {'\<REGION_PROPOSAL>': {'bboxes': [[x1, y1, x2, y2], ...], 
 'labels': ['', '', ...]}}
 ```python
-prompt = <REGION_PROPOSAL>
+prompt = '<REGION_PROPOSAL>'
 run_example(prompt)
 ```