Update readme to add pre-built binary download links (#45)

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/45
Reviewed-by: techknowlogick <[email protected]>
Co-authored-by: Lunny Xiao <[email protected]>
Co-committed-by: Lunny Xiao <[email protected]>

README.md

@@ -1,19 +1,25 @@
 # act runner
 
-Act runner is a runner for Gitea based on [act](https://gitea.com/gitea/act).
+Act runner is a runner for Gitea based on [Gitea fork](https://gitea.com/gitea/act)  of [act](https://github.com/nektos/act) .
 
-## Prerequisites
+## Installation
+
+### Prerequisites
 
 Docker Engine Community version is required. To install Docker CE, follow the official [install instructions](https://docs.docker.com/engine/install/).
 
-## Quickstart
+### Download pre-built binary
 
-### Build
+Visit https://dl.gitea.com/act_runner/ and download the right version for your platform.
+
+### Build from source
 
 ```bash
 make build
 ```
 
+## Quickstart
+
 ### Register
 
 ```bash
@@ -58,4 +64,4 @@ If the registry succeed, it will run immediately. Next time, you could run the r
 
 ```bash
 ./act_runner daemon
-```
+```