add Cargo.lock tweak explanation

Cargo.lock

 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+
+
+# Due to https://git.duniter.org/nodes/rust/duniter-v2s/-/issues/193
+# the lock file cannot be generated entirely automatically.
+# If necessary, follow this process:
+# cargo update
+# git add -p Cargo.lock
+# Accept all modifications except for curve25519-dalek 4.1.1 -> 4.1.2.
+# git reset --hard
+
+
 version = 3
 
 [[package]]