clarify version differences in INSTALL.md (#310)

Close https://github.com/dracula/vim/issues/309

INSTALL.md

@@ -5,28 +5,32 @@
 These are the default instructions using Vim 8's `|packages|` feature. See
 sections below, if you use other plugin managers.
 
-1. Create theme folder (in case you don't have yet):
+1. Create theme folder (in case you don't have it yet):
 
 
 - \*nix:
 ```
+# vim 8.2+
 mkdir -p ~/.vim/pack/themes/start
+# vim 8.0
+mkdir -p ~/.vim/pack/themes/opt
 ```
 
-- Windows: create directory `$HOME\vimfiles\pack\themes\start`
-
-If you use vim 8.0 (and not 8.2), you may need to use `~/.vim/pack/themes/opt`
-or `$HOME\vimfiles\pack\themes\opt` instead.
+- Windows: create directory `$HOME\vimfiles\pack\themes\start` or
+  `$HOME\vimfiles\pack\themes\opt`, according to your version.
 
 2. Navigate to the folder above:
 
 
 - \*nix:
 ```
+# vim 8.2+
 cd ~/.vim/pack/themes/start
+# vim 8.0
+cd ~/.vim/pack/themes/opt
 ```
 
-- Windows: navigate to `$HOME\vimfiles\pack\themes\start`
+- Windows: navigate to the directory you created earlier
 
 3. Clone the repository using the "dracula" name:
 
@@ -38,7 +42,9 @@ git clone https://github.com/dracula/vim.git dracula
 4. Edit your `vimrc` file with the following content:
 
 ```
-packadd! dracula
+if v:version < 802
+    packadd! dracula
+endif
 syntax enable
 colorscheme dracula
 ```
@@ -94,4 +100,6 @@ following in `~/.SpaceVim.d/init.toml`:
 Note that dracula must be in your `'runtimepath'` to load properly: Version 2.0
 introduced autoload functionality for part of the plugin, which doesn't work
 without `'runtimepath'` properly set. Consult your plugin-managers documentation
-to make sure you put dracula on the `'runtimepath'` before loading it.
+to make sure you put dracula on the `'runtimepath'` before loading it. For
+`|packages|`, versions 8.2 and later will autoload `start` packages
+correctly even in your vimrc.