schemas: move README as markdown

This file appears to be intended to be viewed as markdown,
so name it as such.  The 'schema' portion is redundant
considering the path.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I58d6d3c5e7e9fad21ba5c04831fc9ef5d94dba42
diff --git a/schemas/README.schema b/schemas/README.md
similarity index 100%
rename from schemas/README.schema
rename to schemas/README.md