Add PowerShell script to run Docker (#815)

* Add .gitattributes file

* Add PowerShell script to run Docker

.gitattributes

@@ -0,0 +1,4 @@
+*       text=auto
+
+*.sh    text eol=lf
+*.ps1   text eol=crlf

scripts/run-docker.ps1

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+# PowerShell script to build Termux packages with Docker.
+#
+# Usage example:
+#
+# .\scripts\run-docker.ps1 ./build-package.sh -a arm libandroid-support
+
+Set-Variable -Name IMAGE_NAME -Value "termux/package-builder"
+Set-Variable -Name CONTAINER_NAME -Value "termux-package-builder"
+
+Write-Output "Running container ${CONTAINER_NAME} from image ${IMAGE_NAME}..."
+
+docker start $CONTAINER_NAME 2>&1 | Out-Null
+
+if (-Not $?) {
+    Write-Output "Creating new container..."
+    docker run `
+        --detach `
+        --name $CONTAINER_NAME `
+        --volume "${PWD}:/home/builder/termux-packages" `
+        --tty `
+        "$IMAGE_NAME"
+}
+
+if ($args.Count -eq 0) {
+    docker exec --interactive --tty --user builder $CONTAINER_NAME bash
+} else {
+    docker exec --interactive --tty --user builder $CONTAINER_NAME $args
+}