docs: one documentation directory, not two (#137)

docs/ has held the README's images since the fair-launch release. I
added doc/ yesterday for the derivation spec without looking, and #108
then correctly used docs/ -- leaving the repository with both, one
letter apart, which is the kind of thing that quietly costs someone ten
minutes a year forever.

The mistake was mine, so the move is mine: derivation.md and
verify-derivation.py go to docs/, and the two README links follow.

No content changes. The verifier still reproduces the wallet from its
new path, which is the only thing here that can actually break.

1 files changed, 1 insertions, 1 deletions

diff --git a/README.md b/README.md
index 6446b3d..6746e02 100644
--- a/README.md
+++ b/README.md
@@ -107,7 +107,7 @@ words also cover the address the window shows you. **Both still matter** — the
 phrase and the file back up different things, and the difference is where people
 lose money.
 
-The derivation is written down in [doc/derivation.md](doc/derivation.md), with
+The derivation is written down in [docs/derivation.md](docs/derivation.md), with
 test vectors and a script that reproduces them from scratch. It is there so the
 twelve words keep working even if this software does not: paths, address format
 and encoding, enough to recover the keys with ordinary tools and no Bitflash