meta: add keybinding info @ README

Just something people can copy paste quickly

README.md

@@ -7,13 +7,34 @@ No dependencies!
 
 It's available on package control!
 
+## Setting a keybinding
+
+The open the preview, you can search up in the command palette
+(<kbd>ctrl+shift+p</kbd>) `MarkdownLivePreview: Open Preview`. But if you
+prefer to have a shortcut, add this to your keybindings file:
+
+```json
+{
+    "keys": ["alt+m"],
+    "command": "open_markdown_preview"
+}
+```
+
 ## How to contribute
 
 If you know what feature you want to implement, or what bug you wanna fix, then
-go ahead and hack! But if you wanna contribute just to say thanks, and don't
-really know what you could be working on, then there are a bunch of `FIXME`s
-in `MarkdownLivePreview.py` and `markdown2html.py` (GitHub only shows the top
-2 results if you try to search using their interface :slightly_frowning_face:).
+go ahead and hack! Maybe raise an issue before hand so that we can talk about
+it if it's a big feature.
+
+But if you wanna contribute just to say thanks, and don't really know what you
+could be working on, then there are a bunch of `FIXME`s all over this package.
+Just pick one and fix it :-)
+
+```
+$ git clone https://github.com/math2001/MarkdownLivePreview
+$ cd MarkdownLivePreview
+$ grep -R FIXME
+```
 
 ### Hack it!
 
@@ -21,6 +42,4 @@ in `MarkdownLivePreview.py` and `markdown2html.py` (GitHub only shows the top
 2. Make your own branch (the name of the branch should be the feature you are
    implementing eg. `improve-tables`, `fix-crash-on-multiple-preview`
 3. All your code should be formated by black.
-4. Send a PR!
-
-FIXME: add a git hook to format using black (can the git hook be added on github?)
+4. Send a PR!