move full explanation to after erroneous example

Author: bhgomes

compiler/rustc_error_codes/src/error_codes/E0625.md

@@ -1,5 +1,4 @@
-Static and const variables can refer to other const variables. But a const
-variable cannot refer to a thread-local static variable.
+A compile-time const variable is referring to a thread-local static variable.
 
 Erroneous code example:
 
@@ -12,8 +11,10 @@ static X: usize = 12;
 const Y: usize = 2 * X;
 ```
 
-In this example, `Y` cannot refer to `X`. To fix this, the value can be
-extracted as a const and then used:
+Static and const variables can refer to other const variables but a const
+variable cannot refer to a thread-local static variable. In this example,
+`Y` cannot refer to `X`. To fix this, the value can be extracted as a const
+and then used:
 
 ```
 #![feature(thread_local)]