Add tooltips for Import/export buttons and clarify file format

[psobolewskiPhD]

In this PR I add simple tooltips to the buttons, just so it's clear from the UI what these do.
Also, I was curious what the file format is like, so I added that to the docs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.09%. Comparing base (34d3fa9) to head (34e3303).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #127   +/-   ##
=======================================
  Coverage   94.09%   94.09%           
=======================================
  Files          13       13           
  Lines        2099     2099           
=======================================
  Hits         1975     1975           
  Misses        124      124           

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[TimMonko]

Good clarifications. Might be worth adding a mention of import using pip only (I think thats how I understand the code)

[psobolewskiPhD]

import using pip only

I don't think so?
Looks like it calls install_packages which checks the tool to use:

napari-plugin-manager/napari_plugin_manager/base_qt_plugin_dialog.py

Lines 1590 to 1607 in 34d3fa9

	def _install_packages(
	self,
	packages: Sequence[str] = (),
	):
	if not packages:
	_packages = self.direct_entry_edit.text()
	packages = (
	[_packages] if os.path.exists(_packages) else _packages.split()
	)
	self.direct_entry_edit.clear()
	if packages:
	tool = (
	InstallerTools.CONDA
	if self._action_conda.isChecked()
	else InstallerTools.PIP
	)
	self.installer.install(tool, packages)

[TimMonko]

Yes, I goofed. I was thinking I can't install from conda with pip, forgetting I can't test conda without a conda install. I read the code wrong. I shouldn't have hit approve, just comment that it was a good idea to clarify. I was just browsing around, sorry! Still learning how to be helpful.

[goanpeca]

Thanks for working on this @psobolewskiPhD :)