Update last release's CHANGELOG with some tips

[AliSoftware]

Note that we should also think about providing an error message when swiftgen images is passed a non-xcassets directory (instead of making the command line succeed without error but have the generated file contain "// No images found")

\cc @djbe
\ref #175 #214 (imports)
\ref #199 #207 (assets catalogs)
\ref #213 (multiple paths)

[djbe]

We'll have to do this based on the "extension" of the folder, because actool happily tries to parse a folder structure but does not then "dive" into catalog "files", and ignores any other files. Sample output from xcrun actool --print-contents UnitTests/:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>com.apple.actool.catalog-contents</key>
	<array>
		<dict>
			<key>children</key>
			<array>
				<dict>
					<key>filename</key>
					<string>expected</string>
				</dict>
				<dict>
					<key>filename</key>
					<string>Filters</string>
				</dict>
				<dict>
					<key>children</key>
					<array>
						<dict>
							<key>filename</key>
							<string>Fonts</string>
						</dict>
						<dict>
							<key>filename</key>
							<string>Storyboards-iOS</string>
						</dict>
						<dict>
							<key>filename</key>
							<string>Storyboards-OSX</string>
						</dict>
					</array>
					<key>filename</key>
					<string>fixtures</string>
				</dict>
				<dict>
					<key>filename</key>
					<string>TestSuites</string>
				</dict>
			</array>
			<key>filename</key>
			<string>UnitTests</string>
		</dict>
	</array>
</dict>
</plist>

[AliSoftware]

Yeah, I was more thinking about checking each file extension before invoking actool on each of them. I'll let you implement that on the upcoming PR you talked about in #213, so I guess we can merge this one as soon as the CI is ok?

[AliSoftware]

Hahaha for once it's me who misformatted the CHANGELOG 😆

[djbe]

Jup, #217 should be merged alongside this.

[AliSoftware]

Cool!

CI might take some time, it seems like Travis is having issues again: https://www.traviscistatus.com/incidents/nq0sf0srvx8s