README.md: Minor corrections

* **Declarative build instructions/definitions**

* **Declarative build instructions/definitions**

  BuildStream provides a a flexible and extensible framework for the modelling

  BuildStream provides a flexible and extensible framework for the modelling

  of software build pipelines in a declarative YAML format, which allows you to

  of software build pipelines in a declarative YAML format, which allows you to

  manipulate filesystem data in a controlled, reproducible sandboxed environment.

  manipulate filesystem data in a controlled, reproducible sandboxed environment.

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BuildStream operates on a set of YAML files (.bst files), as follows:

BuildStream operates on a set of YAML files (.bst files), as follows:

* loads the YAML files which describe the target(s) and all dependencies

* Loads the YAML files which describe the target(s) and all dependencies.

* evaluates the version information and build instructions to calculate a build

* Evaluates the version information and build instructions to calculate a build

  graph for the target(s) and all dependencies and unique cache-keys for each

  graph for the target(s) and all dependencies and unique cache-keys for each

  element

  element.

* retrieves elements from cache if they are already built, or builds them in a

* Retrieves previously built elements (artifacts) from a local/remote cache, or

  sandboxed environment using the instructions declared in the .bst files

  builds the elements in a sandboxed environment using the instructions declared

* transforms/configures and/or deploys the resulting target(s) based on the

  in the .bst files.

* Transforms/configures and/or deploys the resulting target(s) based on the

  instructions declared in the .bst files.

  instructions declared in the .bst files.