INSTALL.md: move back to root directory to fix Dracula website.

When the INSTALL.md directory was moved from the root of the repository,
it disappeared from the draculatheme.com website. Moving it back should
fix it.

It disappeared because the Dracula website relies on the contents of
INSTALL.md to generate the HTML for the page. When it was moved, it did
not know what to do.

Signed-off-by: Ethan Carter Edwards <[email protected]>

Author: ethancedwards8

docs/INSTALL.md renamed to INSTALL.md

@@ -41,3 +41,7 @@ programs.tmux = {
 1. Make sure  `run -b '~/.tmux/plugins/tpm/tpm'` is at the bottom of your .tmux.conf
 2. Run tmux
 3. Use the tpm install command: `prefix + I` (default prefix is ctrl+b)
+
+#### Configuration
+
+The configuration options are documented on [our GitHub](https://github.com/dracula/tmux/blob/master/docs/CONFIG.md)