Remove .md extensions that break links (#5742)
Remove .md extensions that break links (#5742)

The navigation links at the start of the content on pages such as https://docs.docker.com/get-started/part2/ have broken links (at least, with JavaScript disabled). The links go to e.g. https://docs.docker.com/get-started/part2.md but should instead go to https://docs.docker.com/get-started/part2 or https://docs.docker.com/get-started/part2/ .
docker/docker.github.io,anweiss/docker.github.io,johnstep/docker.github.io,thaJeztah/docker.github.io,JimGalasyn/docker.github.io,londoncalling/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,londoncalling/docker.github.io,JimGalasyn/docker.github.io,anweiss/docker.github.io,johnstep/docker.github.io,docker/docker.github.io,johnstep/docker.github.io,JimGalasyn/docker.github.io,docker/docker.github.io,JimGalasyn/docker.github.io,londoncalling/docker.github.io,londoncalling/docker.github.io,thaJeztah/docker.github.io,anweiss/docker.github.io,JimGalasyn/docker.github.io,londoncalling/docker.github.io,thaJeztah/docker.github.io,anweiss/docker.github.io,thaJeztah/docker.github.io,johnstep/docker.github.io,anweiss/docker.github.io,johnstep/docker.github.io