Update README.md for windows (#95)

Added instructions to help Windows users install the plugin

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## Pre-launch Checklist

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---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: cj-radcliff

README.md

@@ -40,6 +40,35 @@ gemini extensions update flutter
 gemini extensions uninstall flutter
 ```
 
+**Note for Windows users:** There is currently a [known issue](https://github.com/google-gemini/gemini-cli/issues/10616) with installing extensions on Gemini CLI for Windows. The workaround is as follows:
+
+1. Follow instructions above to attempt to install the plugin (this will fail).
+```bash
+    gemini extensions install https://github.com/gemini-cli-extensions/flutter.git
+ ```
+ 
+2. In the command line, navigate to the folder in the home user's path where the code was downloaded (USER is the user's username)
+```bash
+    cd %TEMP%
+```
+ 
+3. Locate the folder for the downloaded extension. It will be the latest titled "gemini-extension<hash>" where <hash> is a 6 character string. Change into this directory.
+```bash
+    cd gemini-extension123456
+```
+
+4. There should be a zip file in this folder called "win32.flutter.zip". Unpack this file using `tar` (available in modern Windows versions) or by right-clicking it in File Explorer and selecting "Extract All...".
+
+```bash
+    tar xvf win32.flutter.zip
+```
+
+5. Use the path flag to gemini installation
+
+```bash
+    gemini extensions install --path %TEMP%\gemini-extension123456
+```
+
 ### 2. Available Commands
 
 The new commands will be available in new Gemini CLI sessions. The following commands will be available (with or without the `flutter:` prefix):