What is the syntax for writing comments in build.gradle file?

Looking down this build.gradle file

apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "21.1.2"

    defaultConfig {
        applicationId "package.myapp"
        minSdkVersion 19
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.nineoldandroids:library:2.4.0'
}

What if I would like to write a comment on why did I chose this library for this project,

what is the syntax for writing comments in build.gradle file?

Easy:

// Single line comment

/*
 Multi
 line
 comment
*/

Use the // or /* */

For example:

        // Top-level build file where you can add configuration options common to all sub-projects/modules.
    
    buildscript {
        repositories {
            jcenter()
        }
        dependencies {
            classpath 'com.android.tools.build:gradle:1.2.3'
    
            // NOTE: Do not place your application dependencies here; they belong
            // in the individual module build.gradle files
        }
    }

/**
 * Returns the credential username used by Namirial Maven repository
 * Set this value in your ~/.gradle/gradle.properties with CREDENTIALS_USERNAME key
 * @return
 */
def getCredentialsMavenUsername() {
    return hasProperty('CREDENTIALS_USERNAME') ? CREDENTIALS_USERNAME : ""
}