Make README logo work in dark mode

Dark mode is, they say, the new thing, and the logo doesn't work super
well with it, because it's black on dark grey.  This is surprisingly
hard to fix.  There are a few options:
- make the logo colored; sorry, but I like black
- add a white border to the logo; this is what Apollo does but I
  think it's pretty ugly in dark mode
- add svg with media queries; this works well but only if the github
  dark mode setting matches the browser(/OS) dark mode setting, since
  that's what the media queries look at
I opted for option 3.  This required converting the text in the SVG to
paths, since it really matters that you have the exact same font.  (I
tested on Android Firefox, which empirically doesn't have the same fonts
I have on desktop.)

Fixes #17.

Issue: #17

Test plan:
tested that it looks good on both mobile firefox in dark mode, and
desktop firefox+chrome in light mode.

Reviewers: dbraley, kevinb, kevindangoor, marksandstrom

Makefile

@@ -6,7 +6,4 @@ check:
 	go run github.com/golangci/golangci-lint/cmd/golangci-lint run ./...
 	go test -cover ./...
 
-docs/images/genqlient.png: docs/images/genqlient.svg
-	convert -density 600 -background transparent "$<" "$@"
-
 .PHONY: example

README.md

@@ -1,4 +1,4 @@
-![generated graphql client ⇒ genqlient](docs/images/genqlient.png)
+<img width="100%" alt="generated graphql client ⇒ genqlient" src="docs/images/genqlient.svg">
 
 # genqlient: a truly type-safe Go GraphQL client
 

docs/images/README.md

@@ -0,0 +1,5 @@
+# genqlient logo
+
+`genqlient-orig.svg` is the original logo.  To create `genqlient.svg`, I:
+- converted all text to paths
+- added media queries to make the paths white if the user is in dark mode (see issue #17)