Fix demo docker pull step

[jeremyrickard]

The current README is broken when trying to use the demo steps

docker run -d -p 5000:5000 --platform linux/amd64 ghcr.io/oras-project/registry:v1.0.0-rc2
Unable to find image 'ghcr.io/oras-project/registry:v1.0.0-rc2' locally
docker: Error response from daemon: manifest unknown.
See 'docker run --help'.

There needs to be a dot in the tag.

crane ls ghcr.io/oras-project/registry
v0.0.1-alpha
v0.0.2-alpha
v0.0.3-alpha
latest
v1.0.0-rc
v1.0.0-rc.2

Tihis PR updates the README:

docker run -d -p 5000:5000 --platform linux/amd64 ghcr.io/oras-project/registry:v1.0.0-rc.2
Unable to find image 'ghcr.io/oras-project/registry:v1.0.0-rc.2' locally
v1.0.0-rc.2: Pulling from oras-project/registry
9621f1afde84: Pull complete
26bf68903cef: Pull complete
1991bda9245a: Pull complete
caa58183a89b: Pull complete
Digest: sha256:d3b10de113cd24404a0e35e6f6949854156a839deb7204fe8dfad9cc9723b1fb
Status: Downloaded newer image for ghcr.io/oras-project/registry:v1.0.0-rc.2
f11cb78ea5f1b3dff68caaae0a736e104df00ec5fe60a12a87f2058f30884455

[shizhMSFT]

LGTM

[codecov-commenter]

Codecov Report

Merging #420 (a9f73c1) into main (f947da5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #420   +/-   ##
=======================================
  Coverage   34.60%   34.60%           
=======================================
  Files          23       23           
  Lines        1254     1254           
=======================================
  Hits          434      434           
  Misses        809      809           
  Partials       11       11           

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[SteveLasker]

LGTM