📝 Add README for OneUptime Infrastructure Agent

Added a README file for the OneUptime Infrastructure Agent providing detailed instructions about installation and usage. The README also includes information about the supported platforms.

README.md

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+# OneUptime Infrastructure Agent (go)
+
+The OneUptime Infrastructure Agent is a lightweight, open-source agent that collects system metrics and sends them to the OneUptime platform. It is designed to be easy to install and use, and to be extensible.
+
+## Installation
+
+```
+curl -O https://tinyurl.com/4cf65czc
+
+# or
+
+curl -O https://raw.githubusercontent.com/anxuanzi/oneuptime-infrastructure-agent-go/main/install.sh
+
+# then run the install script
+
+chmod +x install.sh && ./install.sh
+
+# You can change the host to your own host if you're self hosting the OneUptime platform. 
+# You can find the secret key on OneUptime Dashboard. Click on "View Monitor" and go to "Settings" tab.
+# Install the agent as a systemd service.
+
+oneuptime-infrastructure-agent install --secret-key=YOUR_SECRET_KEY --oneuptime-url=https://oneuptime.com
+```
+
+Once its up and running you should see the metrics on the OneUptime Dashboard.
+
+## Starting the agent
+
+```
+oneuptime-infrastructure-agent start
+```
+
+## Stopping the agent
+
+```
+oneuptime-infrastructure-agent stop
+```
+
+## Restarting the agent
+
+```
+oneuptime-infrastructure-agent restart
+```
+
+## Uninstalling the agent
+
+```
+oneuptime-infrastructure-agent uninstall && rm -rf /usr/bin/oneuptime-infrastructure-agent
+```
+
+## Supported Platforms
+
+- Linux
+- MacOS
+- Windows