fix: manually ignore bazel-* directories to make using custom Bazel builds easier (#1181)

Normally, Bazel will ignore its convenience symlinks, so putting them in
the .bazelignore file isn't necessary. However, when
`--output_user_root` is set, which is beneficial to set when using
different Bazel versions (it preserves the analysis cache between
versions), the symlinks aren't ignored. Putting them in the bazelignore
file fixes this.

.bazelignore

diff --git a/.bazelignore b/.bazelignore
index e69de29..a603a7b 100644
--- a/.bazelignore
+++ b/.bazelignore
@@ -0,0 +1,8 @@
+# Normally these are ignored, but if you're using a custom
+# build of Bazel with a custom --output_user_root value, Bazel
+# tries to follow the symlinks of the other builds and finds
+# the WORKSPACE, BUILD, etc files and tries to build them.
+bazel-rules_python
+bazel-bin
+bazel-out
+bazel-testlogs