docs: improve sentiments example model compatibility

Re-engineer the `sentiments.gpt` example tool body prompt wording so that it works
with `claude-3-opus` and `gemini-1.5`.

Signed-off-by: Nick Hale <[email protected]>

Author: njhale

examples/sentiments.gpt

@@ -1,11 +1,8 @@
 tools: github.com/gptscript-ai/browser, sentiments
 description: get the sentiments expressed in a tweet
-args: url: URL of the tweet to analyze
+parameters: url: URL of the tweet to analyze
 
-Perform the actions in the following order:
-
-Get the text of the tweet referenced by $url.
-Then, analyze the sentiments expressed in this tweet.
+Get the text of the tweet at ${url}. After getting the text, get its sentiments.
 
 ---
 name: sentiments