docs: add example + .vsh script with auto detection of SDL2 version (v…

…lang#516)

* docs: add example with auto detection of SDL2 version

* add setup.vsh, to make matching the installed SDL version easier for users

Add a script to ease the post installation setup of SDL for end users.

* Update README.md

* insert 2.0.8 master at the start of supported_versions

* Update setup.vsh

---------

Co-authored-by: Delyan Angelov <[email protected]>

README.md

@@ -20,6 +20,15 @@ v install sdl
 If you want to use another version of SDL2 you will, currently, have to install
 it via `git` or by manual download.
 
+An example of installing the system provided version of SDL2 via `git`:
+```bash
+git clone https://github.com/vlang/sdl.git ~/.vmodules
+v ~/.vmodules/sdl/setup.vsh
+```
+
+Should `sdl2-config` be absent on your system you can try the following instead,
+by providing the version manually:
+
 An example of installing SDL2 `v2.0.12` via `git`:
 ```bash
 git clone https://github.com/vlang/sdl.git ~/.vmodules

setup.vsh

@@ -0,0 +1,36 @@
+import os
+
+os.chdir(os.dir(os.executable()))!
+
+res := os.execute('sdl2-config --version')
+if res.exit_code != 0 {
+	println('sdl2-config is missing')
+	exit(1)
+}
+system_version := res.output.trim_space()
+println('Your version is ${system_version}')
+
+remotes := os.execute('git branch -r --list')
+if remotes.exit_code != 0 {
+	println('git is missing')
+	exit(1)
+}
+mut supported_versions := remotes.output.split_into_lines().map(it.trim_space()).filter(it.starts_with('origin/2')).map(it.all_after('origin/'))
+supported_versions.insert(0, '2.0.8') // master
+println('The SDL module officially supports these versions of SDL:\n   ${supported_versions}')
+
+if system_version == '2.0.8' {
+	println('Setting up the repository to branch master, that exactly matches your system SDL version 2.0.8')
+	os.system('git checkout master')
+	exit(0)
+}
+
+if system_version in supported_versions {
+	println('Setting up the repository to branch ${system_version} that exactly matches your system SDL version')
+	os.system('git checkout ${system_version}')
+	exit(0)
+}
+
+base_version := '${system_version.all_before_last('.')}.0'
+println('Setting up the repository to branch ${base_version}, that best matches the system SDL version: ${system_version} ...')
+os.system('git checkout ${base_version}')