README: Clean up footnote syntax

It's too similar to link syntax and threw me.

Change-Id: I492e0fad00e72d15bfbd25b707f89bf1bef6a4e5
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/README.md b/README.md
index c9fe6ab..5aae834 100644
--- a/README.md
+++ b/README.md
@@ -48,8 +48,8 @@
 
 ## Working with `libpldm`
 
-Components of the [library ABI][^1] (loosely, functions) are separated into
-three categories:
+Components of the library ABI[^1] (loosely, functions) are separated into three
+categories:
 
 [^1]: ["library API + compiler ABI = library ABI"][libstdc++-library-abi]