Add tutorial on plugins (#36)

Author: awvwgk

pages/tutorial/index.md

@@ -10,4 +10,5 @@ This section contains courses for learning about the usage and fpm at specific e
 :::{toctree}
 hello-fpm
 dependencies
+plugins
 :::

pages/tutorial/plugins.md

@@ -0,0 +1,99 @@
+# Extending fpm with plugins
+
+The Fortran package manager has a plugin system which allows to easily extend its functionality.
+This tutorial will show how to install a plugin with fpm and use it.
+
+
+## Registry search tool
+
+The [fpm-search] project is a plugin to query the package registry.
+Since it is built with fpm we can easily install it on our system with
+
+[fpm-search]: https://github.com/brocolis/fpm-search
+
+```{code-block} text
+git clone https://github.com/brocolis/fpm-search
+cd fpm-search
+fpm install --profile release
+```
+
+This will install the ``fpm-search`` binary to ``~/.local/bin`` (or ``%APPDATA%\local\bin`` on Windows).
+
+:::::{note}
+Ensure that the installed binary is in the ``PATH``, *i.e.* run
+
+```{code-block} text
+which fpm-search
+~/.local/bin/fpm-search
+```
+
+If no binary is found, add the directory to your path using
+
+::::{tab-set}
+:::{tab-item} Bash (Linux)
+
+Default settings for the bash shell can be found in the ``.bashrc`` file in the home directory, to append to the ``PATH`` following the instructions below.
+
+```{code-block} text
+echo "export PATH=$PATH:$HOME/.local/bin" >> ~/.bashrc
+. ~/.bashrc
+```
+
+Make sure to source your ``.bashrc`` after changing it, otherwise the change will not be applied to the current shell.
+:::
+:::{tab-item} Zsh (MacOS)
+
+Default settings for the zsh shell can be found in the ``.zshrc`` file in the home directory, to append to the ``PATH`` use
+
+```{code-block} text
+echo "export PATH=$PATH:$HOME/.local/bin" >> ~/.zshrc
+exec zsh
+```
+
+Make sure to restart zsh after changing the ``.zshrc`` it, otherwise the change will not be applied to the current shell.
+:::
+:::{tab-item} CMD (Windows)
+
+The ``PATH`` variable can be modified using the pathman program from the cmd prompt
+
+```{code-block} text
+pathman /au %APPDATA%\local\bin
+```
+:::
+::::
+:::::
+
+Now with a working installation we can invoke our new plugin from fpm.
+
+```{code-block} text
+❯ fpm search
+Downloading registry ... https://github.com/fortran-lang/fpm-registry/raw/master/index.json
+...
+```
+
+Note that we use ``fpm search`` rather than ``fpm-search`` in the command.
+To find a package for building a command-line interface we can now type
+
+```{code-block} text
+❯ fpm search commandline
+M_CLI : Unix-style commandline parsing using a prototype command and NAMELIST (STD:f2008)
+M_CLI2 : Unix-style commandline parsing using a prototype command
+```
+
+To use one of the packages in our manifest we can generate the necessary dependency line by running
+
+```{code-block} text
+❯ fpm search --toml M_CLI2
+M_CLI2 = { git = "https://github.com/urbanjost/M_CLI2" }
+```
+
+Adding this line to a package manifest allows to depend on the respective project.
+
+:::{admonition} Summary
+:class: tip
+In this tutorial you learned how to
+
+- installing an fpm plugin
+- use the fpm-search plugin to query the registry
+- generate a dependency entry from a query result
+:::