Merge bitcoin/bitcoin#32417: doc: Explain that .gitignore is not for IDE-specific excludes

fada115 doc: Explain that .gitignore is not for IDE-specific excludes (MarcoFalke)

Pull request description:

  This comes up frequently, so document it.

  Examples:

  * bitcoin/bitcoin#27275
  * bitcoin/bitcoin#21894
  * bitcoin/bitcoin#32392
  * bitcoin/bitcoin#17868

  ...

ACKs for top commit:
  l0rinc:
    ACK fada115
  hebasto:
    ACK fada115.
  janb84:
    ACK [fada115](bitcoin/bitcoin@fada115)

Tree-SHA512: 6fd1e48de54b40118a49ef61ad157fea278bba568286a022559a4815e53f26650db98a779a1ea2b3085237ded5cbee20d4c2dd1ef51e6a2d3d6085d7063f5309

Author: hebasto

.gitignore

@@ -1,3 +1,8 @@
+# Patterns that are specific to a text editor, IDE, operating system, or user
+# environment are not added here. They should be added to your local gitignore
+# file instead:
+# https://docs.github.com/en/get-started/git-basics/ignoring-files#configuring-ignored-files-for-all-repositories-on-your-computer
+
 # Build subdirectories.
 /*build*
 !/build-aux