BIP 8: Note LOCKED_IN bit requirement in GBT section

Author: luke-jr

bip-0008.mediawiki

@@ -211,6 +211,7 @@ The template Object is also extended:
 The "version" key of the template is retained, and used to indicate the server's preference of deployments.
 If versionbits is being used, "version" MUST be within the versionbits range of [0x20000000...0x3FFFFFFF].
 Miners MAY clear or set bits in the block version WITHOUT any special "mutable" key, provided they are listed among the template's "vbavailable" and (when clearing is desired) NOT included as a bit in "vbrequired".
+Servers MUST set bits in "vbrequired" for deployments in LOCKED_IN state, to ensure blocks produced are valid.
 
 Softfork deployment names listed in "rules" or as keys in "vbavailable" may be prefixed by a '!' character.
 Without this prefix, GBT clients may assume the rule will not impact usage of the template as-is; typical examples of this would be when previously valid transactions cease to be valid, such as BIPs 16, 65, 66, 68, 112, and 113.