Add installation details and Blender compatibility to README (#358)

- screenshot
- detail instructions
- warning on blender version

README.md

@@ -2,28 +2,31 @@
 
 Native Godot scene format exporter for [Blender](https://www.blender.org), making the
 export process to [Godot Engine](https://godotengine.org) as straightforward as possible.
-
 ___
 
 **Warning:** This exporter is experimental, and still lacks many features.
 If you need a full-featured import-export pipeline, consider using glTF 2.0 instead.
 (The glTF 2.0 exporter is built into Blender.)
 
-___
+**Blender compatibility:** The current `master` branch requires at least Blender 2.80.
 
 ## Installation
 
 1. Copy the `io_scene_godot` directory the location where Blender stores the
-   scripts/addons folder on your system (you should see other io_scene_*
-   folders there from other addons). Copy the entire dir and not just its
-   contents.
+   `scripts/addons` folder on your system. Copy the *entire* directory and not just its
+   contents. For instance, on Linux, add-ons should be installed in
+   `$HOME/.config/blender/<version>/scripts/addons` (create folders as needed).
+   `<version>` should be replaced with your Blender version (such as `2.83`
+   or `2.91` - don't include the letter or patch number if there is one).
+   See [Blender directory layout](https://docs.blender.org/manual/en/latest/advanced/blender_directory_layout.html)
+   for more information.
 2. Go to the Blender settings and enable the "Godot Exporter" plugin.
-3. Export your file with `File` -> `Export` -> `Godot Engine (.escn)`
+   ![Enabling the add-on in the Blender user preferences](install.png)
+3. Export your file with `File` -> `Export` -> `Godot Engine (.escn)`.
 
 If you find bugs or want to suggest improvements, please open an issue on the
 upstream [GitHub repository](https://github.com/godotengine/blender-exporter).
 
-
 ## Usage
 
 See [the documentation](https://docs.godotengine.org/en/stable/getting_started/workflow/assets/escn_exporter/index.html)
@@ -43,15 +46,12 @@ This repository includes a Makefile to assist with development. Running
    [pylint](https://www.pylint.org/) style tests. Your code must pass these to
    be elegible to merge.
 
-
 Current regression tests use the daily build of Blender 2.8 from Blender [official
 site](https://builder.blender.org/download/) and runs on ubuntu 16.04. To fix the
 diff test failure:
    -  You can run a `make export-blends` followed by a `make update-examples` and commit the changes made to the [reference_exports](tests/reference_exports). However, if you are running on a platform different than the one used by the TravisCI, there is a small chance that regression won't be passing because of float rounding. Then you might need to look at the TravisCI log and fix the remaining issue by hand.
    - Or you can use the [update_scene_from_travis.sh](tests/update_scene_from_travis.sh) script, run it with the failing TravisCI job ID as the argument. The script will fetch the scene diffs from the Travis machine to your local git repository and apply it.
 
-
-
 ## License
 
 This Godot exporter is distributed under the terms of the GNU General