Fix Homebrew formula to use HEAD and update docs

[hirotaka]

What's the problem?

When following the README instructions and running brew tap tobi/try, I got this error:

$ brew tap tobi/try
Error: Failure while executing; git clone https://github.com/tobi/homebrew-try /opt/homebrew/Library/Taps/tobi/homebrew-try --origin=origin --template= --config core.fsmonitor=false exited with 128.

This happens because there's no homebrew-try repository. The repo is named try, which doesn't follow Homebrew's naming convention (homebrew-*).

Then I tried brew install try directly instead, I got a SHA256 mismatch error:

$ brew install try
==> Fetching downloads for: try
==> Fetching dependencies for tobi/try/try: openssl@3 and ruby
==> Downloading https://ghcr.io/v2/homebrew/core/openssl/3/manifests/3.6.0
################################################################################################################################################################################## 100.0%
==> Fetching openssl@3
==> Downloading https://ghcr.io/v2/homebrew/core/openssl/3/blobs/sha256:9a8fa2ae1ef3424b116d7e6422d979e0290f4affdef072b1592e4535d2617d92
################################################################################################################################################################################## 100.0%
==> Downloading https://ghcr.io/v2/homebrew/core/ruby/manifests/3.4.6
################################################################################################################################################################################## 100.0%
==> Fetching ruby
==> Downloading https://ghcr.io/v2/homebrew/core/ruby/blobs/sha256:8db26d72de0d97182fa05e1cc48f2e86ab03c040831f2087705fc94eb0d067a0
################################################################################################################################################################################## 100.0%
==> Fetching tobi/try/try
==> Downloading https://github.com/tobi/try/archive/refs/heads/main.tar.gz
==> Downloading from https://codeload.github.com/tobi/try/tar.gz/refs/heads/main
#=#=-  #      #
Error: try: SHA-256 mismatch
Expected: dd3753f38b5c35597c8c2528a19efd7e4289bbbe977d18e2e299a2a57b393a8e
  Actual: 151778fdd07adac23fb021d2d84bd0756e0d626a97498503da24413bfdd72c28
    File: /Users/hirotaka/Library/Caches/Homebrew/downloads/7fef3f3e550762c030552960944b4df9886ae8802c0860c1459dcf5b45ed904a--try-main.tar.gz
To retry an incomplete download, remove the file above.

This is because the formula uses an archive URL for the main branch (archive/refs/heads/main.tar.gz), so the hash changes every time main is updated.

How this fixes it

1. Formula/try.rb: Switch to using head

   • Removed url and sha256 (these were causing the mismatch)
   • Removed version "main" (invalid version string)
   • Added head to reference the main branch directly

2. README.md: Updated with correct installation instructions

   • Fixed to use two-argument brew tap command (explains why full URL is needed)

How to install now

brew tap tobi/try https://github.com/tobi/try
brew install try

I hope it should work now!