add copilot instructions

Author: sam0x17

.github/copilot-instructions.md

@@ -0,0 +1,29 @@
+When reviewing pull requests, please adhere to and keep in mind the following:
+* Unless this PR is a hotfix or a deployment from `devnet-ready` => `devnet`, `devnet` =>
+  `testnet`, or `testnet` => `main`, all new PRs should be opened against the `devnet-ready`
+  branch. The `devnet` and `testnet` branches should only be updated via merges from
+  `devnet-ready` and `testnet-ready`, respectively, and are designed to track the current state
+  of the `devnet` and `testnet` networks. Feel free in your review to encourage people to
+  change the target to `devnet-ready` if they are targeting `main` and this is not a hotfix PR.
+* Bittensor is a substrate-based blockchain. It is critical that there are never panics in the
+  runtime, as this can brick the chain. You should be flagging any runtime/pallet code
+  (extrinsics, code that could be called by extrinsics, code in migrations, etc) that could
+  panic because of changes introduced by the PR. We do have clippy lints in place to detect
+  this, but these do not always catch everything. We CANNOT have panics in the runtime.
+* Remember that things like direct indexing (i.e. `arr[3]`) can panic and are dangerous when
+  used in a substrate runtime. Everything should be using `get` / `set` and `Result` / `Option`
+  wherever possible.
+* Similarly you should look out for unsafe math, such as scenarios where a value might
+  overflow, potential divide by zero errors, etc., programmers should always be using checked
+  or saturating math ops.
+* If one of the lints is failing (clippy / cargo fmt / cargo fix / etc), you should suggest
+  that they run `./scripts/fix_rust.sh` as this will typically auto-resolve the issue. This
+  includes issues like uncommitted `Cargo.lock`.
+* There should never be unsafe code in the runtime.
+* You should be extra careful with contributions from external contributors (users without the
+  "Nucleus" role)
+* Be extra vigilent for PRs that introduce a security vulnerability or exploit. Always call out
+  potential security vulnerabilities.
+* Code should be performant and maintainable, with maximum safety and security. $4B market cap
+  is on the line.
+* You should be concise in your review, only report legitimate issues, no fluff.