fix: update description of X.yaml

Author: AnimeshAgarwal28

spec/std/isa/register_file/X.yaml

@@ -9,9 +9,9 @@ name: X
 long_name: General Purpose Registers
 description: |
   The 'X' register file contains the general-purpose integer registers. Each register
-  is MXLEN bits wide, unless XLEN<MXLEN. Register 'x0' is hardwired to zero, while
-  the remaining registers hold architecturally visible integer state used by the
-  calling convention and execution environment.
+  is MXLEN bits wide, but will appear to be XLEN bits wide if XLEN<MXLEN. Register 
+  'x0' is hardwired to zero, while the remaining registers hold architecturally 
+  visible integer state used by the calling convention and execution environment.
 definedBy: I
 register_class: general_purpose
 register_length: MXLEN