Restrict Users to have only one post ..!!

I am creating an application where User will login into their account (using devise gem for authentication) and add their personal details/upload documents and obviously every user have their personal accounts/identities. In addition I want to hide "new link" in index.html.erb file.
Later on I will add Admin Banckend (using active admin gem) and only admin can see all the documents/details and can download the same.

Here is my code for testing :-

post_controller.rb

class PostsController < ApplicationController
  before_action :set_post, only: [:show, :edit, :update, :destroy]
  before_action :authenticate_user!

  def index
    @posts = Post.all
  end

  def show
  end

  def new
    @post = current_user.posts.build
  end

  def edit
  end

  def create
    @post = current_user.posts.build(post_params)

    respond_to do |format|
      if @post.save
        format.html { redirect_to @post, notice: 'Post was successfully created.' }
        format.json { render :show, status: :created, location: @post }
      else
        format.html { render :new }
        format.json { render json: @post.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /posts/1
  # PATCH/PUT /posts/1.json
  def update
    respond_to do |format|
      if @post.update(post_params)
        format.html { redirect_to @post, notice: 'Post was successfully updated.' }
        format.json { render :show, status: :ok, location: @post }
      else
        format.html { render :edit }
        format.json { render json: @post.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /posts/1
  # DELETE /posts/1.json
  def destroy
    @post.destroy
    respond_to do |format|
      format.html { redirect_to posts_url, notice: 'Post was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_post
      @post = Post.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def post_params
      params.require(:post).permit(:title, :content)
    end
end

index.html.erb

<p id="notice"><%= notice %></p>

<h1>Listing Posts</h1>

<table>
  <thead>
    <tr>
      <th>Title</th>
      <th>Content</th>
      <th colspan="3"></th>
    </tr>
  </thead>
        <td><%= current_user.post.try(:title) %></td>
        <td><%= current_user.post.try(:content) %></td>
</table>

<br>


  <%= link_to 'New Post', new_post_path %>

Please help me to do this.