branch hinting: reword the byte offset description

"function body" is unclear, and actually at odds with the definition in
the core spec. The byte offset is relative to the start of the locals vector

Author: yuri91

document/metadata/code/binary.rst

@@ -32,7 +32,7 @@ section of format *T*.
    \end{array}
 .. index:: ! code metadata section
 
-Where :math:`\X{off}` is the byte offset of the annotation starting from the beginning of the function body, and :math:`\X{data}` is a further payload, whose content depends on the format :math:`T`.
+Where :math:`\X{off}` is the byte offset of the attached instruction, relative to the beginning of the |Bfunc| declaration, and :math:`\X{data}` is a further payload, whose content depends on the format :math:`T`.
 
 |Bcodemetadatafunc| entries must appear in order of increasing :math:`x`, and duplicate id values are not allowed. |Bcodemetadata| entries must appear in order of increasing :math:`\X{off}`, and duplicate offset values are not allowed.
 

proposals/branch-hinting/Overview.md

@@ -100,7 +100,7 @@ and a function index can appear at most once.
 
 Each *branch hint* structure consists of
 
-* the |U32| byte offset of the hinted instruction from the beginning of the function body,
+* the |U32| byte offset of the hinted instruction, relative to the beginning of the function locals declaration,
 * A |U32| with value `1`,
 * a |U32| indicating the meaning of the hint: