readme: Improve file size units

Since a lowercase m technically stands for milli and not mega, and the
lowercase b for bits, it's misleading. This changes mb to MB, and kb to
kB.

README.md

@@ -9,7 +9,7 @@
 - **:paintbrush: Splash Theming**: Easy theming for your splash which works with most themes for any client mod
 - **:electric_plug: Drop-in**: Replace one file and it's installed, that's it (same with uninstall)
 - **:gear: Configurable**: Adds many config options for Discord and OpenAsar enhancements (see config section)
-- **:feather: Lightweight**: <1% of Discord's original size (9mb -> ~50kb)
+- **:feather: Lightweight**: <1% of Discord's original size (9 MB -> ~50 kB)
 - **:shield: No Tracking**: Removes Discord's built-in tracking for crashes and errors in the asar (not app itself)
 
 ### See [FAQ](faq.md) for more details
@@ -20,4 +20,4 @@
 
 
 ## Config
-You can configure OpenAsar by clicking the "OpenAsar..." version info in the bottom of your settings sidebar, which will open the config window.
+You can configure OpenAsar by clicking the "OpenAsar..." version info in the bottom of your settings sidebar, which will open the config window.