feat: Add AppData manifest and Linux desktop file

Related: VirusTotal#14

com.virustotal.VirusTotalUploader.appdata.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<component type="desktop-application">
+    <id>com.virustotal.VirusTotalUploader</id>
+    <name>VirusTotal Uploader</name>
+    <summary>Upload files to virustotal.com</summary>
+    <description>
+        <p>
+            This program internally uses the VirusTotal public API.
+            You can drag and drop a file or folder into the program to queue
+            it for uploading and scanning.
+        </p>
+    </description>
+    <categories>
+        <category>Network</category>
+        <category>Security</category>
+    </categories>
+    <metadata_license>CC0-1.0</metadata_license>
+    <project_license>Apache-2.0</project_license>
+    <url type="homepage">https://www.virustotal.com/ru/documentation/desktop-applications/linux-oss-uploader</url>
+    <url type="bugtracker">https://github.com/VirusTotal/qt-virustotal-uploader/issues</url>
+    <launchable type="desktop-id">com.virustotal.VirusTotalUploader.desktop</launchable>
+    <screenshots>
+        <screenshot type="default">
+            <image>https://virustotalcloud.appspot.com/static/img/osx-uploader/osx-app-screen.png</image>
+        </screenshot>
+    </screenshots>
+</component>

com.virustotal.VirusTotalUploader.desktop

@@ -0,0 +1,7 @@
+[Desktop Entry]
+Type=Application
+Name=VirusTotal Uploader
+Exec=VirusTotalUploader
+Icon=com.virustotal.VirusTotalUploader
+Terminal=false
+Categories=Network;Security;