Update documentation to explain account tier access (#4)

Author: corbindavenport

README.md

@@ -2,7 +2,7 @@
 
 Alt Text Creator is a browser extension that generates [alternate text](https://en.wikipedia.org/wiki/Alt_attribute) for images using the [GPT-4o or GPT-4o Mini model](https://platform.openai.com/docs/guides/vision) from OpenAI. You can right-click on any image and select "Create Alt Text" to generate the text, which is then copied to your clipboard.
 
-**You must supply your own API key from OpenAI for the extension to work.** Alt Text Creator uses the Low Resolution mode in the API and local caching to reduce the per-image processing cost. The [current pricing](https://openai.com/pricing#:~:text=Vision%20pricing%20calculator) is available on OpenAI's website.
+**You must supply your own API key from OpenAI and be on [usage tier 1](https://help.openai.com/en/articles/7102672-how-can-i-access-gpt-4-gpt-4-turbo-gpt-4o-and-gpt-4o-mini#:~:text=usage%20tier%201) for the extension to work.** Alt Text Creator uses the Low Resolution mode in the API and local caching to reduce the per-image processing cost. The [current pricing](https://openai.com/pricing#:~:text=Vision%20pricing%20calculator) is available on OpenAI's website.
 
 [**Download for Google Chrome**](https://chromewebstore.google.com/detail/alt-text-creator-with-gpt/nlahkceofkdggfgfpheakpaphdfplaio)
 

main.html

@@ -53,7 +53,7 @@ <h2>Settings</h2>
 				<!-- How to use -->
 				<h2>How to use</h2>
 				<p>This extension uses the <a href="https://platform.openai.com/docs/guides/vision" target="_blank">GPT-4o</a> large language model to generate <a href="https://en.wikipedia.org/wiki/Alt_attribute" target="_blank">alternate text</a> for any image, which is read by search engines, screen readers, and other tools. You can right-click on any image and select "Generate Alt Text" to generate alternative text for an image. After a few seconds, a notification will appear with the generated text, which is automatically copied to your clipboard.</p>
-				<p>You must <a href="https://platform.openai.com/api-keys" target="_blank">create an OpenAI API key</a> and paste it in the below settings. OpenAI charges for API access after free credit runs out, and you can <a href="https://openai.com/pricing#:~:text=Vision%20pricing%20calculator" target="_blank">check current pricing</a> from the OpenAI website (and click the "Low Resolution" checkbox). This extension uses the Low Resolution mode and caches responses locally to reduce costs as much as possible.</p>
+				<p>You must supply your own <a href="https://platform.openai.com/api-keys" target="_blank">API key</a> from OpenAI and <a href="https://help.openai.com/en/articles/7102672-how-can-i-access-gpt-4-gpt-4-turbo-gpt-4o-and-gpt-4o-mini#:~:text=usage%20tier%201" target="_blank">unlock usage tier 1 on your OpenAI account</a> for the extension to work. OpenAI charges for API access after free credit runs out, and you can <a href="https://openai.com/pricing#:~:text=Vision%20pricing%20calculator" target="_blank">check current pricing</a> from the OpenAI website (click the "Low Resolution" checkbox). This extension uses the Low Resolution mode and caches responses locally to reduce costs as much as possible.</p>
 				<p>The generated alternate text might be incorrect sometimes. Be sure to always follow <a href="https://support.microsoft.com/en-us/office/everything-you-need-to-know-to-write-effective-alt-text-df98f884-ca3d-456c-807b-1a1fa82f5dc2">best practices for writing alt text</a>!</p>
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