feat: add initial 'dev' section with docker build explanation

content/docs/dev/_index.md

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+title = "Developer guides"
+weight = 5
+summary = "NSM in-depth details and help for developers"
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content/docs/dev/build.md

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+title = "Build docker images"
+weight = 1
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+
+# Build docker images
+
+All Network Service Mesh applications are located in separate repositories and has [cmd prefix](https://github.com/networkservicemesh?q=cmd&type=all&language=&sort=). Next, look at exist ways to build image for `cmd` repositories.
+
+## Docker build
+
+Each `cmd` NSM repository has a Dockerfile. In most cases recommends use `docker build .` relative to the repository.
+
+
+## Docker build with custom dependencies
+
+For some cases we need to modify NSM dependencies of `cmd` application. In this case could be used different tactics with its pros and cons.
+
+### Use a forked dependency
+
+To simply build a docker image with changed code in NSM dependencies could be use a [fork](https://docs.github.com/en/get-started/quickstart/fork-a-repo) dependencies.
+
+
+Example:
+
+1. Push the change into the fork (myrepo/sdk) as a branch `my-branch`.
+2. Use `go get -u myrepo/sdk@my-branch.` Note: Go will find the dependency and prints the `$version` of it, but returns an error as well. 
+3. Write into go.mod of the repositry a replace directive `replace nsm/sdk => myrepo/sdk "$version"`
+4. Run `docker build .`
+
+
+### Use a local folder
+
+Alternative way to add changed code into cmd could be using a `./local` folder that contains vendored dependencies. After that need to put the local replace into the go.mod.
+
+
+Example:
+
+1. mkdir local
+2. cd local
+3. git clone  git@github.com:edwarnicke/sdk.git
+4. cd sdk
+5. git remote add upstream git@github.com:networkservicemesh/sdk.git
+6. cd ../..
+7. Add a replace directive `replace nsm/sdk => ./local/myrepo/sdk`
+