add README

README.md

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+# Nix development environments, for various languages
+
+Those of us on NixOS never install language toolkits system-wide, unlike other distros.
+Regrettably, many projects are not taking advantage of Nix for reproducible development environments. You should
+make a big fuss about this in every open source project you are a part of and constantly evangelize about Nix.
+Until Nix is universally adopted, this repository serves as a collection of flakes which provides compilers,
+package managers, and basic development tools like LSPs for common languages. Simply clone this to a desired location,
+then run:
+
+```bash
+nix develop <location-of-repo>#<language>
+
+# example
+nix develop ~/.devenvs#rustNightly
+
+# provides rust-analyzer, rustc, cargo, and some others from nightly toolchain
+```
+
+## Automatic environment loading
+
+For convenience, you can use [nix-direnv](https://github.com/nix-community/nix-direnv) to
+automatically load these environments.
+
+Simply add the following `.envrc` to the project directory:
+
+```bash
+# file: .envrc
+use flake <path-to-this-repo>#<language>
+```
+
+Example:
+
+```bash
+use flake ~/.devenvs#go
+```
+
+If you don't want to commit these files, make sure to run the following:
+
+```bash
+# tell git to ignore these direnv files for this local repository
+git update-index --skip-worktree .envrc .direnv
+```
+