android: add F-Droid metadata file and fdroidserver package to guix environment

.fdroid.yml

@@ -0,0 +1,28 @@
+Categories:
+  - Internet
+License: GPL-3.0-or-later
+WebSite: https://forge.monarch-pass.net/malacoda/piecannon
+SourceCode: https://forge.monarch-pass.net/malacoda/piecannon
+IssueTracker: https://forge.monarch-pass.net/malacoda/piecannon/issues
+
+Name: PieCannon
+Summary: File sharing tool
+Description: Tool for sharing files through the web.
+
+RepoType: git
+Repo:  https://forge.monarch-pass.net/malacoda/piecannon
+
+Builds:
+  - versionName: "1.0"
+    versionCode: 1
+    commit: HEAD
+    build:
+        - mvn clean install -f ../lib/pom.xml
+        - mvn clean install
+    subdir: android
+    output: target/*.apk
+
+AutoUpdateMode: None
+UpdateCheckMode: RepoManifest
+CurrentVersion: "1.0"
+CurrentVersionCode: 1