rename "known bugs" to "caveats"

Turns out neither of these remaining issues are bugs per se; they are
both tradeoffs. Keep them here still, since the default behavior will
probably still surprise a lot of Go developers.

Author: mvdan

README.md

@@ -169,9 +169,9 @@ jobs:
 
 * To report bugs: https://github.community/t5/GitHub-Actions/bd-p/actions
 
-## Known bugs
+## Caveats
 
-* https://github.community/t5/GitHub-Actions/git-config-core-autocrlf-should-default-to-false/m-p/30445 and https://github.com/actions/checkout/issues/135
+* https://github.com/actions/checkout/issues/135
 
 `git config core.autocrlf` defaults to true, so be careful about CRLF endings in
 your plaintext `testdata` files on Windows. To work around this, set up the
@@ -181,7 +181,7 @@ following `.gitattributes`:
 * -text
 ```
 
-* https://github.community/t5/GitHub-Actions/TEMP-is-broken-on-Windows/m-p/30432/thread-id/427 and https://github.com/actions/runner/issues/424
+* https://github.com/actions/runner/issues/424
 
 `os.TempDir` on Windows will contain a short name, since `%TEMP%` also contains
 it. Note that case sensitivity doesn't matter, and that `os.Open` should still