Rename keyboard-level readmes to lower-case (#10759)

This is the recommendation in the [PR
Checklist](https://docs.qmk.fm/#/pr_checklist?id=keyboard-prs) and it
will make working with them easier in the CLI/API/etc.

keyboards/handwired/xealousbrown/readme.md

@@ -0,0 +1,17 @@
+# XealouS Brown
+
+My first handwired keyboard. Originally used TMK, now ported in full glory to QMK.
+
+Build log at:
+https://sites.google.com/site/xaelous/keyboards/handwired-keyboard
+
+Make example for this keyboard (after setting up your build environment):
+
+    make handwired/xealousbrown:default
+
+
+The brief list of speedhacks to make this keyboard blazing fast:
+1) bit-bash implementation of scanning rows, columns. Very short delay between pin waiting.
+2) Compiling with a few extra flags
+3) Eager-per-key Debouncing algorithm (no 5ms delay before message is sent)
+4) 1000hz polling