Add build script into Makefile (#16)

#### What this PR does?

Add build script into Makefile to build the theme conviniently. See README.md for more.

/kind feature

```release-note
None
```

.gitignore

@@ -23,3 +23,4 @@ node_modules
 
 .gradle
 build
+dist

Makefile

@@ -0,0 +1,13 @@
+build: clean
+	echo "Building theme"
+	pnpm install
+	pnpm build
+	echo "Theme built successfully!"
+	echo "Collect theme dist"
+	mkdir dist
+	cp -r templates dist
+	cp theme.yaml settings.yaml README.md dist
+
+clean:
+	echo "Clean dist folder"
+	rm -rf dist

README.md

@@ -1,3 +1,10 @@
 # theme-earth
 
 Default theme for Halo 2.0(WIP)
+
+## Build theme
+
+> If you are using Windows OS, please install `make` command and execute `make` in Git Bash or WSL.
+
+- Execute command `make build` to generate dist folder
+- Zip the dist folder and upload to your Halo

build.gradle

@@ -1,3 +1,4 @@
+// This script is only for IntelliSense of thymeleaf.
 plugins {
   id 'java'
 }