[Keymap] Contra - QWERTY US basic layout; MechWild Marcuio - EN update layout (#16787)

Co-authored-by: Joel Challis <git@zvecr.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: Stephon Parker <stephonparker@Stephons-MacBook-Pro.local>

keyboards/mechwild/mercutio/keymaps/fearless_spiff_en/readme.md

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+Fearless Spiff's Custom Mercutio Keymap
+  - "Programmer"-centric and German layout based keymap
+  - Based on Bongocat and Jonavin keymap
+
+Features
+  - Fancy Bongocat! Yay! (borrowed from bongocat obviously)
+  - Encoder selectable key codes and displayed on OLED (borrowed and multi-line-enhanced from Jonavin)
+    - Change encoder_keys in keymap.c to assign your desired key selection
+  - Additional encoder functionality 
+    - While holding FN_1, page up and down
+    - While holding FN_2, volume up and down
+  - Use my templates for your own layout overview at [Keyboard Layout Editor](http://www.keyboard-layout-editor.com) using my gist [here](https://gist.github.com/FearlessSpiff)
+
+QWERT Layer
+![image](https://user-images.githubusercontent.com/1927259/148683284-04932e15-a34d-451e-b657-335780033f36.png)
+
+FN_1 Layer
+![image](https://user-images.githubusercontent.com/1927259/148683299-f2c80403-3f29-4ba8-9fc4-957729f30b05.png)
+
+FN_2 layer
+![image](https://user-images.githubusercontent.com/1927259/148683306-364bc59c-b41b-4092-b93b-d7b4fc58567b.png)
+