Merge bitcoin/bitcoin#30996: doc: update signet documentation related to build directories

a647d44 doc: update signet documentation related to build directories (Torkel Rogstad)

Pull request description:

  While setting up my own signet I noticed that the binary paths in the documentation for this is out of date, after build artifacts moved to the `build` directory. This PR mimics what happened in #30741

ACKs for top commit:
  maflcko:
    lgtm ACK a647d44
  pablomartin4btc:
    ACK a647d44
  tdb3:
    Code review and light test ACK a647d44

Tree-SHA512: ac7c3806e0ff65860c41d7b7bdad538368d8a6d8d289c10f9714804f963bafd3a9658301b6697f110f5462a92826b62770963508d5eebf88bf9a0a8442d9f72d

Author: fanquake

contrib/signet/README.md

@@ -23,17 +23,16 @@ miner
 
 You will first need to pick a difficulty target. Since signet chains are primarily protected by a signature rather than proof of work, there is no need to spend as much energy as possible mining, however you may wish to choose to spend more time than the absolute minimum. The calibrate subcommand can be used to pick a target appropriate for your hardware, eg:
 
-    cd src/
-    MINER="../contrib/signet/miner"
-    GRIND="./bitcoin-util grind"
+    MINER="./contrib/signet/miner"
+    GRIND="./build/src/bitcoin-util grind"
     $MINER calibrate --grind-cmd="$GRIND"
     nbits=1e00f403 for 25s average mining time
 
 It defaults to estimating an nbits value resulting in 25s average time to find a block, but the --seconds parameter can be used to pick a different target, or the --nbits parameter can be used to estimate how long it will take for a given difficulty.
 
 To mine the first block in your custom chain, you can run:
 
-    CLI="./bitcoin-cli -conf=mysignet.conf"
+    CLI="./build/src/bitcoin-cli -conf=mysignet.conf"
     ADDR=$($CLI -signet getnewaddress)
     NBITS=1e00f403
     $MINER --cli="$CLI" generate --grind-cmd="$GRIND" --address="$ADDR" --nbits=$NBITS